# perf-top

## NAME



           perf-top - System profiling tool.
    


## SYNOPSIS



           _perf top_ [-e <EVENT> | --event=EVENT] [<options>]
    


## DESCRIPTION



           This command generates and displays a performance counter profile
           in real time.
    


## OPTIONS



           -a, --all-cpus
               System-wide collection. (default)
    
           -c <count>, --count=<count>
               Event period to sample.
    
           -C <cpu-list>, --cpu=<cpu>
               Monitor only on 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
               monitor all CPUS.
    
           -d <seconds>, --delay=<seconds>
               Number of seconds to delay between refreshes.
    
           -e <event>, --event=<event>
               Select the PMU event. Selection can be a symbolic event name
               (use _perf list_ to list all events) or a raw PMU event in the
               form of rN where N is a hexadecimal value that represents the
               raw register encoding with the layout of the event control
               registers as described by entries in
               /sys/bus/event_source/devices/cpu/format/*.
    
           --filter=<filter>
               Event filter. This option should follow an event selector
               (-e). For syntax see perf-record(1).
    
           -E <entries>, --entries=<entries>
               Display this many functions.
    
           -f <count>, --count-filter=<count>
               Only display functions with more events than this.
    
           --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.
    
           -F <freq>, --freq=<freq>
               Profile at this frequency. Use _max_ to use the currently
               maximum allowed frequency, i.e. the value in the
               kernel.perf_event_max_sample_rate sysctl.
    
           -i, --inherit
               Child tasks do not inherit counters.
    
           -k <path>, --vmlinux=<path>
               Path to vmlinux. Required for annotation functionality.
    
           --ignore-vmlinux
               Ignore vmlinux files.
    
           --kallsyms=<file>
               kallsyms pathname
    
           -m <pages>, --mmap-pages=<pages>
               Number of mmap data pages (must be a power of two) or size
               specification in bytes with appended unit character - B/K/M/G.
               The size is rounded up to the nearest power-of-two page value.
    
           -p <pid>, --pid=<pid>
               Profile events on existing Process ID (comma separated list).
    
           -t <tid>, --tid=<tid>
               Profile events on existing thread ID (comma separated list).
    
           -u, --uid=
               Record events in threads owned by uid. Name or number.
    
           -r <priority>, --realtime=<priority>
               Collect data with this RT SCHED_FIFO priority.
    
           --sym-annotate=<symbol>
               Annotate this symbol.
    
           -K, --hide_kernel_symbols
               Hide kernel symbols.
    
           -U, --hide_user_symbols
               Hide user symbols.
    
           --demangle-kernel
               Demangle kernel symbols.
    
           -D, --dump-symtab
               Dump the symbol table used for profiling.
    
           -v, --verbose
               Be more verbose (show counter open errors, etc).
    
           -z, --zero
               Zero history across display updates.
    
           -s, --sort
               Sort by key(s): pid, comm, dso, symbol, parent, srcline,
               weight, local_weight, abort, in_tx, transaction, overhead,
               sample, period. Please see description of --sort in the
               perf-report man page.
    
           --fields=
               Specify output field - multiple keys can be specified in CSV
               format. Following fields are available: overhead,
               overhead_sys, overhead_us, overhead_children, sample and
               period. Also it can contain any sort key(s).
    
                   By default, every sort keys not specified in --field will be appended
                   automatically.
    
           -n, --show-nr-samples
               Show a column with the number of samples.
    
           --show-total-period
               Show a column with the sum of periods.
    
           --dsos
               Only consider symbols in these dsos. This option will affect
               the percentage of the overhead column. See --percentage for
               more info.
    
           --comms
               Only consider symbols in these comms. This option will affect
               the percentage of the overhead column. See --percentage for
               more info.
    
           --symbols
               Only consider these symbols. This option will affect the
               percentage of the overhead column. See --percentage for more
               info.
    
           -M, --disassembler-style=
               Set disassembler style for objdump.
    
           --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.
    
           --source
               Interleave source code with assembly code. Enabled by default,
               disable with --no-source.
    
           --asm-raw
               Show raw instruction encoding of assembly instructions.
    
           -g
               Enables call-graph (stack chain/backtrace) recording.
    
           --call-graph [mode,type,min[,limit],order[,key][,branch]]
               Setup and enable call-graph (stack chain/backtrace) recording,
               implies -g. See --call-graph section in perf-record and
               perf-report man pages for details.
    
           --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
               -g/--call-graph option enabled. 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.
    
                   Default: /proc/sys/kernel/perf_event_max_stack when present, 127 otherwise.
    
           --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.
    
           --percent-limit
               Do not show entries which have an overhead under that percent.
               (Default: 0).
    
           --percentage
               Determine how to display the overhead percentage of filtered
               entries. Filters can be applied by --comms, --dsos and/or
               --symbols 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.
    
           -w, --column-widths=<width[,width...]>
               Force each column width to the provided list, for large
               terminal readability. 0 means no limit (default behavior).
    
           --proc-map-timeout
               When processing pre-existing threads /proc/XXX/mmap, it may
               take a long time, because the file may be huge. A time out is
               needed in such cases. This option sets the time out limit. The
               default value is 500 ms.
    
           -b, --branch-any
               Enable taken branch stack sampling. Any type of taken branch
               may be sampled. This is a shortcut for --branch-filter any.
               See --branch-filter for more infos.
    
           -j, --branch-filter
               Enable taken branch stack sampling. Each sample captures a
               series of consecutive taken branches. The number of branches
               captured with each sample depends on the underlying hardware,
               the type of branches of interest, and the executed code. It is
               possible to select the types of branches captured by enabling
               filters. For a full list of modifiers please see the perf
               record manpage.
    
                   The option requires at least one branch type among any, any_call, any_ret, ind_call, cond.
                   The privilege levels may be omitted, in which case, the privilege levels of the associated
                   event are applied to the branch filter. Both kernel (k) and hypervisor (hv) privilege
                   levels are subject to permissions.  When sampling on multiple events, branch stack sampling
                   is enabled for all the sampling events. The sampled branch type is the same for all events.
                   The various filters must be specified as a comma separated list: --branch-filter any_ret,u,k
                   Note that this feature may not be available on all processors.
    
           --branch-history
               Add the addresses of sampled taken branches to the callstack.
               This allows to examine the path the program took to each
               sample.
    
           --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
    
           --overwrite
               Enable this to use just the most recent records, which helps
               in high core count machines such as Knights Landing/Mill, but
               right now is disabled by default as the pausing used in this
               technique is leading to loss of metadata events such as
               PERF_RECORD_MMAP which makes _perf top_ unable to resolve
               samples, leading to lots of unknown samples appearing on the
               UI. Enable this if you are in such machines and profiling a
               workload that doesn’t creates short lived threads and/or
               doesn’t uses many executable mmap operations. Work is being
               planed to solve this situation, till then, this will remain
               disabled by default.
    
           --force
               Don’t do ownership validation.
    
           --num-thread-synthesize
               The number of threads to run when synthesizing events for
               existing processes. By default, the number of threads equals
               to the number of online CPUs.
    
           --namespaces
               Record events of type PERF_RECORD_NAMESPACES and display it
               with the _cgroup_id_ sort key.
    
           -G name, --cgroup name
               monitor only in the container (cgroup) called "name". This
               option is available only in per-cpu mode. The cgroup
               filesystem must be mounted. All threads belonging to container
               "name" are monitored when they run on the monitored CPUs.
               Multiple cgroups can be provided. Each cgroup is applied to
               the corresponding event, i.e., first cgroup to first event,
               second cgroup to second event and so on. It is possible to
               provide an empty cgroup (monitor all the time) using, e.g., -G
               foo,,bar. Cgroups must have corresponding events, i.e., they
               always refer to events defined earlier on the command line. If
               the user wants to track multiple events for a specific cgroup,
               the user can use _-e e1 -e e2 -G foo,foo_ or just use _-e e1 -e_
               _e2 -G foo_.
    
           --all-cgroups
               Record events of type PERF_RECORD_CGROUP and display it with
               the _cgroup_ sort key.
    
           --switch-on EVENT_NAME
               Only consider events after this event is found.
    
                   E.g.:
    
                   Find out where broadcast packets are handled
    
                   perf probe -L icmp_rcv
    
                   Insert a probe there:
    
                   perf probe icmp_rcv:59
    
                   Start perf top and ask it to only consider the cycles events when a
                   broadcast packet arrives This will show a menu with two entries and
                   will start counting when a broadcast packet arrives:
    
                   perf top -e cycles,probe:icmp_rcv --switch-on=probe:icmp_rcv
    
                   Alternatively one can ask for a group and then two overhead columns
                   will appear, the first for cycles and the second for the switch-on event.
    
                   perf top -e '{cycles,probe:icmp_rcv}' --switch-on=probe:icmp_rcv
    
                   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 use the above
                   examples replacing probe:icmp_rcv with the just-after-init 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 top_ 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 top_ with no events
               explicitly specified does.
    
           --stitch-lbr
               Show callgraph with stitched LBRs, which may have more
               complete callgraph. The option must be used with --call-graph
               lbr recording. 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.
    


## INTERACTIVE PROMPTING KEYS



           [d]
               Display refresh delay.
    
           [e]
               Number of entries to display.
    
           [E]
               Event to display when multiple counters are active.
    
           [f]
               Profile display filter (>= hit count).
    
           [F]
               Annotation display filter (>= % of total).
    
           [s]
               Annotate symbol.
    
           [S]
               Stop annotation, return to full profile display.
    
           [K]
               Hide kernel symbols.
    
           [U]
               Hide user symbols.
    
           [z]
               Toggle event count zeroing across display updates.
    
           [qQ]
               Quit.
    
           Pressing any unmapped key displays a menu, and prompts for input.
    


## 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.
    


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