# perf-report

## NAME



           perf-report - Read perf.data (created by perf record) and display
           the profile
    


## SYNOPSIS



           _perf report_ [-i <file> | --input=file]
    


## DESCRIPTION



           This command displays the performance counter profile information
           recorded via perf record.
    


## OPTIONS



           -i, --input=
               Input file name. (default: perf.data unless stdin is a fifo)
    
           -v, --verbose
               Be more verbose. (show symbol address, etc)
    
           -q, --quiet
               Do not show any warnings or messages. (Suppress -v)
    
           -n, --show-nr-samples
               Show the number of samples for each symbol
    
           --show-cpu-utilization
               Show sample percentage for different cpu modes.
    
           -T, --threads
               Show per-thread event counters. The input data file should be
               recorded with -s option.
    
           -c, --comms=
               Only consider symbols in these comms. CSV that understands
               **file://filename******entries. This option will affect the
               percentage of the overhead and latency columns. See
               --percentage for more info.
    
           --pid=
               Only show events for given process ID (comma separated list).
    
           --tid=
               Only show events for given thread ID (comma separated list).
    
           -d, --dsos=
               Only consider symbols in these dsos. CSV that understands**file://filename******entries. This option will affect the
               percentage of the overhead and latency columns. See
               --percentage for more info.
    
           -S, --symbols=
               Only consider these symbols. CSV that understands**file://filename******entries. This option will affect the
               percentage of the overhead and latency columns. See
               --percentage for more info.
    
           --symbol-filter=
               Only show symbols that match (partially) with this filter.
    
           -U, --hide-unresolved
               Only display entries resolved to a symbol.
    
           --parallelism
               Only consider these parallelism levels. Parallelism level is
               the number of threads that actively run on CPUs at the time of
               sample. The flag accepts single number, comma-separated list,
               and ranges (for example: "1", "7,8", "1,64-128"). This is
               useful in understanding what a program is doing during
               sequential/low-parallelism phases as compared to
               high-parallelism phases. This option will affect the
               percentage of the overhead and latency columns. See
               --percentage for more info. Also see the ‘CPU and latency
               overheads’ section for more details.
    
           --latency
               Show latency-centric profile rather than the default
               CPU-consumption-centric profile (requires perf record
               --latency flag).
    
           -s, --sort=
               Sort histogram entries by given key(s) - multiple keys can be
               specified in CSV format. Following sort keys are available:
               pid, comm, dso, symbol, parent, cpu, socket, srcline, weight,
               local_weight, cgroup_id, addr.
    
                   Each key has following meaning:
    
               •   comm: command (name) of the task which can be read via
                   /proc/ <pid>/comm
    
               •   pid: command and tid of the task
    
               •   tgid: command and tgid of the task
    
               •   dso: name of library or module executed at the time of
                   sample
    
               •   dso_size: size of library or module executed at the time
                   of sample
    
               •   symbol: name of function executed at the time of sample
    
               •   symbol_size: size of function executed at the time of
                   sample
    
               •   parent: name of function matched to the parent regex
                   filter. Unmatched entries are displayed as "[other]".
    
               •   cpu: cpu number the task ran at the time of sample
    
               •   socket: processor socket number the task ran at the time
                   of sample
    
               •   parallelism: number of running threads at the time of
                   sample
    
               •   srcline: filename and line number executed at the time of
                   sample. The DWARF debugging info must be provided.
    
               •   srcfile: file name of the source file of the samples.
                   Requires dwarf information.
    
               •   weight: Event specific weight, e.g. memory latency or
                   transaction abort cost. This is the global weight.
    
               •   local_weight: Local weight version of the weight above.
    
               •   cgroup_id: ID derived from cgroup namespace device and
                   inode numbers.
    
               •   cgroup: cgroup pathname in the cgroupfs.
    
               •   transaction: Transaction abort flags.
    
               •   overhead: CPU overhead percentage of sample.
    
               •   latency: latency (wall-clock) overhead percentage of
                   sample. See the ‘CPU and latency overheads’ section for
                   more details.
    
               •   overhead_sys: CPU overhead percentage of sample running in
                   system mode
    
               •   overhead_us: CPU overhead percentage of sample running in
                   user mode
    
               •   overhead_guest_sys: CPU overhead percentage of sample
                   running in system mode on guest machine
    
               •   overhead_guest_us: CPU overhead percentage of sample
                   running in user mode on guest machine
    
               •   sample: Number of sample
    
               •   period: Raw number of event count of sample
    
               •   time: Separate the samples by time stamp with the
                   resolution specified by --time-quantum (default 100ms).
                   Specify with overhead and before it.
    
               •   code_page_size: the code page size of sampled code address
                   (ip)
    
               •   ins_lat: Instruction latency in core cycles. This is the
                   global instruction latency
    
               •   local_ins_lat: Local instruction latency version
    
               •   p_stage_cyc: On powerpc, this presents the number of
                   cycles spent in a pipeline stage. And currently supported
                   only on powerpc.
    
               •   addr: (Full) virtual address of the sampled instruction
    
               •   retire_lat: On X86, this reports pipeline stall of this
                   instruction compared to the previous instruction in
                   cycles. And currently supported only on X86
    
               •   simd: Flags describing a SIMD operation. "e" for empty Arm
                   SVE predicate. "p" for partial Arm SVE predicate
    
               •   type: Data type of sample memory access.
    
               •   typeoff: Offset in the data type of sample memory access.
    
               •   symoff: Offset in the symbol.
    
               •   weight1: Average value of event specific weight (1st field
                   of weight_struct).
    
               •   weight2: Average value of event specific weight (2nd field
                   of weight_struct).
    
               •   weight3: Average value of event specific weight (3rd field
                   of weight_struct).
    
                       By default, overhead, comm, dso and symbol keys are used.
                       (i.e. --sort overhead,comm,dso,symbol).
    
                       If --branch-stack option is used, following sort keys are also
                       available:
    
               •   dso_from: name of library or module branched from
    
               •   dso_to: name of library or module branched to
    
               •   symbol_from: name of function branched from
    
               •   symbol_to: name of function branched to
    
               •   srcline_from: source file and line branched from
    
               •   srcline_to: source file and line branched to
    
               •   mispredict: "N" for predicted branch, "Y" for mispredicted
                   branch
    
               •   in_tx: branch in TSX transaction
    
               •   abort: TSX transaction abort.
    
               •   cycles: Cycles in basic block
    
                       And default sort keys are changed to comm, dso_from, symbol_from, dso_to
                       and symbol_to, see '--branch-stack'.
    
                       When the sort key symbol is specified, columns "IPC" and "IPC Coverage"
                       are enabled automatically. Column "IPC" reports the average IPC per function
                       and column "IPC coverage" reports the percentage of instructions with
                       sampled IPC in this function. IPC means Instruction Per Cycle. If it's low,
                       it indicates there may be a performance bottleneck when the function is
                       executed, such as a memory access bottleneck. If a function has high overhead
                       and low IPC, it's worth further analyzing it to optimize its performance.
    
                       If the --mem-mode option is used, the following sort keys are also available
                       (incompatible with --branch-stack):
                       symbol_daddr, dso_daddr, locked, tlb, mem, snoop, dcacheline, blocked.
    
               •   symbol_daddr: name of data symbol being executed on at the
                   time of sample
    
               •   dso_daddr: name of library or module containing the data
                   being executed on at the time of the sample
    
               •   locked: whether the bus was locked at the time of the
                   sample
    
               •   tlb: type of tlb access for the data at the time of the
                   sample
    
               •   mem: type of memory access for the data at the time of the
                   sample
    
               •   snoop: type of snoop (if any) for the data at the time of
                   the sample
    
               •   dcacheline: the cacheline the data address is on at the
                   time of the sample
    
               •   phys_daddr: physical address of data being executed on at
                   the time of sample
    
               •   data_page_size: the data page size of data being executed
                   on at the time of sample
    
               •   blocked: reason of blocked load access for the data at the
                   time of the sample
    
                       And the default sort keys are changed to local_weight, mem, sym, dso,
                       symbol_daddr, dso_daddr, snoop, tlb, locked, blocked, local_ins_lat,
                       see '--mem-mode'.
    
                       If the data file has tracepoint event(s), following (dynamic) sort keys
                       are also available:
                       trace, trace_fields, [<event>.]<field>[/raw]
    
               •   trace: pretty printed trace output in a single column
    
               •   trace_fields: fields in tracepoints in separate columns
    
               •   <field name>: optional event and field name for a specific
                   field
    
                       The last form consists of event and field names.  If event name is
                       omitted, it searches all events for matching field name.  The matched
                       field will be shown only for the event has the field.  The event name
                       supports substring match so user doesn't need to specify full subsystem
                       and event name everytime.  For example, 'sched:sched_switch' event can
                       be shortened to 'switch' as long as it's not ambiguous.  Also event can
                       be specified by its index (starting from 1) preceded by the '%'.
                       So '%1' is the first event, '%2' is the second, and so on.
    
                       The field name can have '/raw' suffix which disables pretty printing
                       and shows raw field value like hex numbers.  The --raw-trace option
                       has the same effect for all dynamic sort keys.
    
                       The default sort keys are changed to 'trace' if all events in the data
                       file are tracepoint.
    
           -F, --fields=
               Specify output field - multiple keys can be specified in CSV
               format. Following fields are available: overhead, latency,
               overhead_sys, overhead_us, overhead_children, sample, period,
               weight1, weight2, weight3, ins_lat, p_stage_cyc and
               retire_lat. The last 3 names are alias for the corresponding
               weights. When the weight fields are used, they will show the
               average value of the weight.
    
                   Also it can contain any sort key(s).
    
                   By default, every sort keys not specified in -F will be appended
                   automatically.
    
                   If the keys starts with a prefix '+', then it will append the specified
                   field(s) to the default field order. For example: perf report -F +period,sample.
    
           -p, --parent=<regex>
               A regex filter to identify parent. The parent is a caller of
               this function and searched through the callchain, thus it
               requires callchain information recorded. The pattern is in the
               extended regex format and defaults to "^sys_|^do_page_fault",
               see _--sort parent_.
    
           -x, --exclude-other
               Only display entries with parent-match.
    
           -w, --column-widths=<width[,width...]>
               Force each column width to the provided list, for large
               terminal readability. 0 means no limit (default behavior).
    
           -t, --field-separator=
               Use a special separator character and don’t pad with spaces,
               replacing all occurrences of this separator in symbol names
               (and other output) with a _._  character, that thus it’s the
               only non valid separator.
    
           -D, --dump-raw-trace
               Dump raw trace in ASCII.
    
           --disable-order
               Disable raw trace ordering.
    
           -g,
           --call-graph=<print_type,threshold[,print_limit],order,sort_key[,branch],value>
               Display call chains using type, min percent threshold, print
               limit, call order, sort key, optional branch and value. Note
               that ordering is not fixed so any parameter can be given in an
               arbitrary order. One exception is the print_limit which should
               be preceded by threshold.
    
                   print_type can be either:
                   - flat: single column, linear exposure of call chains.
                   - graph: use a graph tree, displaying absolute overhead rates. (default)
                   - fractal: like graph, but displays relative rates. Each branch of
                            the tree is considered as a new profiled object.
                   - folded: call chains are displayed in a line, separated by semicolons
                   - none: disable call chain display.
    
                   threshold is a percentage value which specifies a minimum percent to be
                   included in the output call graph.  Default is 0.5 (%).
    
                   print_limit is only applied when stdio interface is used.  It's to limit
                   number of call graph entries in a single hist entry.  Note that it needs
                   to be given after threshold (but not necessarily consecutive).
                   Default is 0 (unlimited).
    
                   order can be either:
                   - callee: callee based call graph.
                   - caller: inverted caller based call graph.
                   Default is 'caller' when --children is used, otherwise 'callee'.
    
                   sort_key can be:
                   - function: compare on functions (default)
                   - address: compare on individual code addresses
                   - srcline: compare on source filename and line number
    
                   branch can be:
                   - branch: include last branch information in callgraph when available.
                             Usually more convenient to use --branch-history for this.
    
                   value can be:
                   - percent: display overhead percent (default)
                   - period: display event period
                   - count: display event count
    
           --children
               Accumulate callchain of children to parent entry so that then
               can show up in the output. The output will have a new
               "Children" column and will be sorted on the data. It requires
               callchains are recorded. See the ‘Overhead calculation’
               section for more details. Enabled by default, disable with
               --no-children.
    
           --max-stack
               Set the stack depth limit when parsing the callchain, anything
               beyond the specified depth will be ignored. This is a
               trade-off between information loss and faster processing
               especially for workloads that can have a very long callchain
               stack. Note that when using the --itrace option the
               synthesized callchain size will override this value if the
               synthesized callchain size is bigger.
    
                   Default: 127
    
           -G, --inverted
               alias for inverted caller based call graph.
    
           --ignore-callees=<regex>
               Ignore callees of the function(s) matching the given regex.
               This has the effect of collecting the callers of each such
               function into one place in the call-graph tree.
    
           --pretty=<key>
               Pretty printing style. key: normal, raw
    
           --stdio
               Use the stdio interface.
    
           --stdio-color
               _always_ , _never_ or _auto_ , allowing configuring color output via
               the command line, in addition to via "color.ui" .perfconfig.
               Use _--stdio-color always_ to generate color even when
               redirecting to a pipe or file. Using just _--stdio-color_ is
               equivalent to using _always_.
    
           --tui
               Use the TUI interface, that is integrated with annotate and
               allows zooming into DSOs or threads, among other features. Use
               of --tui requires a tty, if one is not present, as when piping
               to other commands, the stdio interface is used.
    
           --gtk
               Use the GTK2 interface.
    
           -k, --vmlinux=<file>
               vmlinux pathname
    
           --ignore-vmlinux
               Ignore vmlinux files.
    
           --kallsyms=<file>
               kallsyms pathname
    
           -m, --modules
               Load module symbols. WARNING: This should only be used with -k
               and a LIVE kernel.
    
           -f, --force
               Don’t do ownership validation.
    
           --symfs=<directory>
               Look for files with symbols relative to this directory.
    
           -C, --cpu
               Only report samples for the list of CPUs provided. Multiple
               CPUs can be provided as a comma-separated list with no space:
               0,1. Ranges of CPUs are specified with -: 0-2. Default is to
               report samples on all CPUs.
    
           -M, --disassembler-style=
               Set disassembler style for objdump.
    
           --source
               Interleave source code with assembly code. Enabled by default,
               disable with --no-source.
    
           --asm-raw
               Show raw instruction encoding of assembly instructions.
    
           --show-total-period
               Show a column with the sum of periods.
    
           -I, --show-info
               Display extended information about the perf.data file. This
               adds information which may be very large and thus may clutter
               the display. It currently includes: cpu and numa topology of
               the host system.
    
           -b, --branch-stack
               Use the addresses of sampled taken branches instead of the
               instruction address to build the histograms. To generate
               meaningful output, the perf.data file must have been obtained
               using perf record -b or perf record --branch-filter xxx where
               xxx is a branch filter option. perf report is able to
               auto-detect whether a perf.data file contains branch stacks
               and it will automatically switch to the branch view mode,
               unless --no-branch-stack is used.
    
           --branch-history
               Add the addresses of sampled taken branches to the callstack.
               This allows to examine the path the program took to each
               sample. The data collection must have used -b (or -j) and -g.
    
                   Also show with some branch flags that can be:
                   - Predicted: display the average percentage of predicated branches.
                                (predicated number / total number)
                   - Abort: display the number of tsx aborted branches.
                   - Cycles: cycles in basic block.
    
               •   iterations: display the average number of iterations in
                   callchain list.
    
           --addr2line=<path>
               Path to addr2line binary.
    
           --objdump=<path>
               Path to objdump binary.
    
           --prefix=PREFIX, --prefix-strip=N
               Remove first N entries from source file path names in
               executables and add PREFIX. This allows to display source code
               compiled on systems with different file system layout.
    
           --group
               Show event group information together. It forces group output
               also if there are no groups defined in data file.
    
           --group-sort-idx
               Sort the output by the event at the index n in group. If n is
               invalid, sort by the first event. It can support multiple
               groups with different amount of events. WARNING: This should
               be used on grouped events.
    
           --demangle
               Demangle symbol names to human readable form. It’s enabled by
               default, disable with --no-demangle.
    
           --demangle-kernel
               Demangle kernel symbol names to human readable form (for C++
               kernels).
    
           --mem-mode
               Use the data addresses of samples in addition to instruction
               addresses to build the histograms. To generate meaningful
               output, the perf.data file must have been obtained using perf
               record -d -W and using a special event -e cpu/mem-loads/p or
               -e cpu/mem-stores/p. See _perf mem_ for simpler access.
    
           --percent-limit
               Do not show entries which have an overhead under that percent.
               (Default: 0). Note that this option also sets the percent
               limit (threshold) of callchains. However the default value of
               callchain threshold is different than the default value of
               hist entries. Please see the --call-graph option for details.
    
           --percentage
               Determine how to display the CPU and latency overhead
               percentage of filtered entries. Filters can be applied by
               --comms, --dsos, --symbols and/or --parallelism options and
               Zoom operations on the TUI (thread, dso, etc).
    
                   "relative" means it's relative to filtered entries only so that the
                   sum of shown entries will be always 100%.  "absolute" means it retains
                   the original value before and after the filter is applied.
    
           --header
               Show header information in the perf.data file. This includes
               various information like hostname, OS and perf version,
               cpu/mem info, perf command line, event list and so on.
               Currently only --stdio output supports this feature.
    
           --header-only
               Show only perf.data header (forces --stdio).
    
           --time
               Only analyze samples within given time window: <start>,<stop>.
               Times have the format seconds.nanoseconds. If start is not
               given (i.e. time string is _,x.y_) then analysis starts at the
               beginning of the file. If stop time is not given (i.e. time
               string is _x.y,_) then analysis goes to end of file. Multiple
               ranges can be separated by spaces, which requires the argument
               to be quoted e.g. --time "1234.567,1234.789 1235,"
    
                   Also support time percent with multiple time ranges. Time string is
                   'a%/n,b%/m,...' or 'a%-b%,c%-%d,...'.
    
                   For example:
                   Select the second 10% time slice:
    
                   perf report --time 10%/2
    
                   Select from 0% to 10% time slice:
    
                   perf report --time 0%-10%
    
                   Select the first and second 10% time slices:
    
                   perf report --time 10%/1,10%/2
    
                   Select from 0% to 10% and 30% to 40% slices:
    
                   perf report --time 0%-10%,30%-40%
    
           --switch-on EVENT_NAME
               Only consider events after this event is found.
    
                   This may be interesting to measure a workload only after some initialization
                   phase is over, i.e. insert a perf probe at that point and then using this
                   option with that probe.
    
           --switch-off EVENT_NAME
               Stop considering events after this event is found.
    
           --show-on-off-events
               Show the --switch-on/off events too. This has no effect in
               _perf report_ now but probably we’ll make the default not to
               show the switch-on/off events on the --group mode and if there
               is only one event besides the off/on ones, go straight to the
               histogram browser, just like _perf report_ with no events
               explicitly specified does.
    
           --itrace
               Options for decoding instruction tracing data. The options
               are:
    
                   i       synthesize instructions events
                   y       synthesize cycles events
                   b       synthesize branches events
                   c       synthesize branches events (calls only)
                   r       synthesize branches events (returns only)
                   x       synthesize transactions events
                   w       synthesize ptwrite events
                   p       synthesize power events (incl. PSB events for Intel PT)
                   o       synthesize other events recorded due to the use
                           of aux-output (refer to perf record)
                   I       synthesize interrupt or similar (asynchronous) events
                           (e.g. Intel PT Event Trace)
                   e       synthesize error events
                   d       create a debug log
                   f       synthesize first level cache events
                   m       synthesize last level cache events
                   M       synthesize memory events
                   t       synthesize TLB events
                   a       synthesize remote access events
                   g       synthesize a call chain (use with i or x)
                   G       synthesize a call chain on existing event records
                   l       synthesize last branch entries (use with i or x)
                   L       synthesize last branch entries on existing event records
                   s       skip initial number of events
                   q       quicker (less detailed) decoding
                   A       approximate IPC
                   Z       prefer to ignore timestamps (so-called "timeless" decoding)
                   T       use the timestamp trace as kernel time
    
                   The default is all events i.e. the same as --itrace=iybxwpe,
                   except for perf script where it is --itrace=ce
    
                   In addition, the period (default 100000, except for perf script where it is 1)
                   for instructions events can be specified in units of:
    
                   i       instructions
                   t       ticks
                   ms      milliseconds
                   us      microseconds
                   ns      nanoseconds (default)
    
                   Also the call chain size (default 16, max. 1024) for instructions or
                   transactions events can be specified.
    
                   Also the number of last branch entries (default 64, max. 1024) for
                   instructions or transactions events can be specified.
    
                   Similar to options g and l, size may also be specified for options G and L.
                   On x86, note that G and L work poorly when data has been recorded with
                   large PEBS. Refer linkperf:perf-intel-pt[1] man page for details.
    
                   It is also possible to skip events generated (instructions, branches, transactions,
                   ptwrite, power) at the beginning. This is useful to ignore initialization code.
    
                   --itrace=i0nss1000000
    
                   skips the first million instructions.
    
                   The 'e' option may be followed by flags which affect what errors will or
                   will not be reported. Each flag must be preceded by either '+' or '-'.
                   The flags are:
                           o       overflow
                           l       trace data lost
    
                   If supported, the 'd' option may be followed by flags which affect what
                   debug messages will or will not be logged. Each flag must be preceded
                   by either '+' or '-'. The flags are:
                           a       all perf events
                           e       output only on errors (size configurable - see linkperf:perf-config[1])
                           o       output to stdout
    
                   If supported, the 'q' option may be repeated to increase the effect.
    
                   To disable decoding entirely, use --no-itrace.
    
           --full-source-path
               Show the full path for source files for srcline output.
    
           --show-ref-call-graph
               When multiple events are sampled, it may not be needed to
               collect callgraphs for all of them. The sample sites are
               usually nearby, and it’s enough to collect the callgraphs on a
               reference event. So user can use "call-graph=no" event
               modifier to disable callgraph for other events to reduce the
               overhead. However, perf report cannot show callgraphs for the
               event which disable the callgraph. This option extends the
               perf report to show reference callgraphs, which collected by
               reference event, in no callgraph event.
    
           --stitch-lbr
               Show callgraph with stitched LBRs, which may have more
               complete callgraph. The perf.data file must have been obtained
               using perf record --call-graph lbr. Disabled by default. In
               common cases with call stack overflows, it can recreate better
               call stacks than the default lbr call stack output. But this
               approach is not foolproof. There can be cases where it creates
               incorrect call stacks from incorrect matches. The known
               limitations include exception handing such as setjmp/longjmp
               will have calls/returns not match.
    
           --socket-filter
               Only report the samples on the processor socket that match
               with this filter
    
           --samples=N
               Save N individual samples for each histogram entry to show
               context in perf report tui browser.
    
           --raw-trace
               When displaying traceevent output, do not use print fmt or
               plugins.
    
           -H, --hierarchy
               Enable hierarchical output. In the hierarchy mode, each sort
               key groups samples based on the criteria and then sub-divide
               it using the lower level sort key.
    
                   For example:
                   In normal output:
    
                   perf report -s dso,sym
                   # Overhead  Shared Object      Symbol
                       50.00%  [kernel.kallsyms]  [k] kfunc1
                       20.00%  perf               [.] foo
                       15.00%  [kernel.kallsyms]  [k] kfunc2
                       10.00%  perf               [.] bar
                        5.00%  libc.so            [.] libcall
    
                   In hierarchy output:
    
                   perf report -s dso,sym --hierarchy
                   #   Overhead  Shared Object / Symbol
                       65.00%    [kernel.kallsyms]
                         50.00%    [k] kfunc1
                         15.00%    [k] kfunc2
                       30.00%    perf
                         20.00%    [.] foo
                         10.00%    [.] bar
                        5.00%    libc.so
                          5.00%    [.] libcall
    
           --inline
               If a callgraph address belongs to an inlined function, the
               inline stack will be printed. Each entry is function name or
               file/line. Enabled by default, disable with --no-inline.
    
           --mmaps
               Show --tasks output plus mmap information in a format similar
               to /proc/<PID>/maps.
    
                   Please note that not all mmaps are stored, options affecting which ones
                   are include 'perf record --data', for instance.
    
           --ns
               Show time stamps in nanoseconds.
    
           --stats
               Display overall events statistics without any further
               processing. (like the one at the end of the perf report -D
               command)
    
           --tasks
               Display monitored tasks stored in perf data. Displaying
               pid/tid/ppid plus the command string aligned to distinguish
               parent and child tasks.
    
           --percent-type
               Set annotation percent type from following choices:
               global-period, local-period, global-hits, local-hits
    
                   The local/global keywords set if the percentage is computed
                   in the scope of the function (local) or the whole data (global).
                   The period/hits keywords set the base the percentage is computed
                   on - the samples period or the number of samples (hits).
    
           --time-quantum
               Configure time quantum for time sort key. Default 100ms.
               Accepts s, us, ms, ns units.
    
           --total-cycles
               When --total-cycles is specified, it supports sorting for all
               blocks by _Sampled Cycles%_. This is useful to concentrate on
               the globally hottest blocks. In output, there are some new
               columns:
    
                   'Sampled Cycles%' - block sampled cycles aggregation / total sampled cycles
                   'Sampled Cycles'  - block sampled cycles aggregation
                   'Avg Cycles%'     - block average sampled cycles / sum of total block average
                                       sampled cycles
                   'Avg Cycles'      - block average sampled cycles
                   'Branch Counter'  - block branch counter histogram (with -v showing the number)
    
           --skip-empty
               Do not print 0 results in the --stat output.
    


## CPU AND LATENCY OVERHEADS



           There are two notions of time: wall-clock time and CPU time. For a
           single-threaded program, or a program running on a single-core
           machine, these notions are the same. However, for a
           multi-threaded/multi-process program running on a multi-core
           machine, these notions are significantly different. Each second of
           wall-clock time we have number-of-cores seconds of CPU time. Perf
           can measure overhead for both of these times (shown in _overhead_
           and _latency_ columns for CPU and wall-clock time correspondingly).
    
           Optimizing CPU overhead is useful to improve _throughput_ , while
           optimizing latency overhead is useful to improve _latency_. It’s
           important to understand which one is useful in a concrete
           situation at hand. For example, the former may be useful to
           improve max throughput of a CI build server that runs on 100% CPU
           utilization, while the latter may be useful to improve
           user-perceived latency of a single interactive program build.
           These overheads may be significantly different in some cases. For
           example, consider a program that executes function _foo_ for 9
           seconds with 1 thread, and then executes function _bar_ for 1 second
           with 128 threads (consumes 128 seconds of CPU time). The CPU
           overhead is: _foo_ - 6.6%, _bar_ - 93.4%. While the latency overhead
           is: _foo_ - 90%, _bar_ - 10%. If we try to optimize running time of
           the program looking at the (wrong in this case) CPU overhead, we
           would concentrate on the function _bar_ , but it can yield only 10%
           running time improvement at best.
    
           By default, perf shows only CPU overhead. To show latency
           overhead, use _perf record --latency_ and _perf report_ :
    
               .ft C
               Overhead  Latency  Command
                 93.88%   25.79%  cc1
                  1.90%   39.87%  gzip
                  0.99%   10.16%  dpkg-deb
                  0.57%    1.00%  as
                  0.40%    0.46%  sh
               .ft
    
           To sort by latency overhead, use _perf report --latency_ :
    
               .ft C
               Latency  Overhead  Command
                39.87%     1.90%  gzip
                25.79%    93.88%  cc1
                10.16%     0.99%  dpkg-deb
                 4.17%     0.29%  git
                 2.81%     0.11%  objtool
               .ft
    
           To get insight into the difference between the overheads, you may
           check parallelization histogram with
           _--sort=latency,parallelism,comm,symbol --hierarchy_ flags. It shows
           fraction of (wall-clock) time the workload utilizes different
           numbers of cores (_Parallelism_ column). For example, in the
           following case the workload utilizes only 1 core most of the time,
           but also has some highly-parallel phases, which explains
           significant difference between CPU and wall-clock overheads:
    
               .ft C
                 Latency  Overhead     Parallelism / Command / Symbol
               +  56.98%     2.29%     1
               +  16.94%     1.36%     2
               +   4.00%    20.13%     125
               +   3.66%    18.25%     124
               +   3.48%    17.66%     126
               +   3.26%     0.39%     3
               +   2.61%    12.93%     123
               .ft
    
           By expanding corresponding lines, you may see what
           commands/functions run at the given parallelism level:
    
               .ft C
                 Latency  Overhead     Parallelism / Command / Symbol
               -  56.98%     2.29%     1
                     32.80%     1.32%     gzip
                      4.46%     0.18%     cc1
                      2.81%     0.11%     objtool
                      2.43%     0.10%     dpkg-source
                      2.22%     0.09%     ld
                      2.10%     0.08%     dpkg-genchanges
               .ft
    
           To see the normal function-level profile for particular
           parallelism levels (number of threads actively running on CPUs),
           you may use _--parallelism_ filter. For example, to see the profile
           only for low parallelism phases of a workload use _--latency_
           _--parallelism=1-2_ flags.
    


## OVERHEAD CALCULATION



           The CPU overhead can be shown in two columns as _Children_ and _Self_
           when perf collects callchains (and corresponding _Wall_ columns for
           wall-clock overhead). The _self_ overhead is simply calculated by
           adding all period values of the entry - usually a function
           (symbol). This is the value that perf shows traditionally and sum
           of all the _self_ overhead values should be 100%.
    
           The _children_ overhead is calculated by adding all period values of
           the child functions so that it can show the total overhead of the
           higher level functions even if they don’t directly execute much.
           _Children_ here means functions that are called from another
           (parent) function.
    
           It might be confusing that the sum of all the _children_ overhead
           values exceeds 100% since each of them is already an accumulation
           of _self_ overhead of its child functions. But with this enabled,
           users can find which function has the most overhead even if
           samples are spread over the children.
    
           Consider the following example; there are three functions like
           below.
    
               .ft C
               void foo(void) {
                   /* do something */
               }
    
               void bar(void) {
                   /* do something */
                   foo();
               }
    
               int main(void) {
                   bar()
                   return 0;
               }
               .ft
    
           In this case _foo_ is a child of _bar_ , and _bar_ is an immediate child
           of _main_ so _foo_ also is a child of _main_. In other words, _main_ is a
           parent of _foo_ and _bar_ , and _bar_ is a parent of _foo_.
    
           Suppose all samples are recorded in _foo_ and _bar_ only. When it’s
           recorded with callchains the output will show something like below
           in the usual (self-overhead-only) output of perf report:
    
               .ft C
               Overhead  Symbol
               ........  .....................
                 60.00%  foo
                         |
                         --- foo
                             bar
                             main
                             __libc_start_main
    
                 40.00%  bar
                         |
                         --- bar
                             main
                             __libc_start_main
               .ft
    
           When the --children option is enabled, the _self_ overhead values of
           child functions (i.e. _foo_ and _bar_) are added to the parents to
           calculate the _children_ overhead. In this case the report could be
           displayed as:
    
               .ft C
               Children      Self  Symbol
               ........  ........  ....................
                100.00%     0.00%  __libc_start_main
                         |
                         --- __libc_start_main
    
                100.00%     0.00%  main
                         |
                         --- main
                             __libc_start_main
    
                100.00%    40.00%  bar
                         |
                         --- bar
                             main
                             __libc_start_main
    
                 60.00%    60.00%  foo
                         |
                         --- foo
                             bar
                             main
                             __libc_start_main
               .ft
    
           In the above output, the _self_ overhead of _foo_ (60%) was add to the
           _children_ overhead of _bar_ , _main_ and ___libc_start_main_. Likewise,
           the _self_ overhead of _bar_ (40%) was added to the _children_ overhead
           of _main_ and _\_\_libc_start_main_.
    
           So _\_\_libc_start_main_ and _main_ are shown first since they have
           same (100%) _children_ overhead (even though they have zero _self_
           overhead) and they are the parents of _foo_ and _bar_.
    
           Since v3.16 the _children_ overhead is shown by default and the
           output is sorted by its values. The _children_ overhead is disabled
           by specifying --no-children option on the command line or by
           adding _report.children = false_ or _top.children = false_ in the perf
           config file.
    


* * *