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<s>[INST] What is MLC tool? [/INST] The Memory Latency Checker (MLC) is a tool used for measuring memory latencies and bandwidth on Intel architectures. It's primarily used by system administrators, developers, and performance tuning professionals to assess the performance of memory subsystems in servers and other Inte... |
<s>[INST] What does MLC tool measure? [/INST] When Intel® MLC is launched without any additional parameters, it automatically identifies the system topology and measures the following (a screen shot is shown for each):
1. A matrix of idle memory latencies for requests originating from each of the sockets and addressed ... |
<s>[INST] what is idle latency and how to measure it? [/INST] Idle latency is also known as unloaded latency. Basically, when the latency is measured, the system is mostly idle with no other application or workload running. Idle latency is measured by doing dependent loads similar to pointer chasing). A buffer is init... |
<s>[INST] how does MLC measure bandwidth [/INST] For measuring b/w, MLC executes load instructions that are not consumed (i.e the data that is returned as part of the load is not consumed in any subsequent instructions). This allows MLC to generate maximum possible b/w. MLC spawns one s/w thread on each of the configur... |
<s>[INST] how does mlc measure loaded latency [/INST] One of the main features of Intel® MLC is measuring how latency changes as b/w demand increases. To facilitate this, MLC creates several threads where the number of threads matches the number of logical CPUs minus 1. These threads are used to generate the bandwidth.... |
<s>[INST] how does MLC measures cache-to-cache transfer latency [/INST] MLC supports measuring cache-to-cache transfer latencies. The basic idea is to bring in lines into L1/L2/L3 and then transfer control to another thread (which is either running on another core on the same socket or a different socket). This thread ... |
<s>[INST] what are the command line parameters that MLC provides [/INST] MLC provides the following command line arguments:
1. latency matrix [./mlc --latency_matrix]
2. bandwidth matrix [./mlc --bandwidth_matrix]
3. peak injection bandwidth [./mlc --peak_injection_bandwidth]
4. max bandwidth [./mlc --max_bandwidth]
5.... |
<s>[INST] what is the -a flag [/INST] -a Measure idle latencies from each of the available CPUs. This option is valid only in latency_matrix mode. It goes with --idle_latency and --latency_matrix arguments. </s> |
<s>[INST] what is the -b flag [/INST] Select the size of the buffer (in KB) to be allocated by each CPU. Default is 200,000 KB for latency measurements and 100,000 KB for b/w measurements. In case of b/w measurements with both read and write traffic, same size buffer will be allocated11 once for reads and once for writ... |
<s>[INST] what is the -B flag [/INST] Print per-thread bandwidth numbers. Default is to print the total b/w generated across all the threads only. This option is valid only in loaded_latency mode. </s> |
<s>[INST] what is the -c flag [/INST] Pin the latency-measuring thread to a particular CPU. All memory accesses will be initiated from this CPU irrespective of where the memory that is being addressed is located. This option is valid in idle_latency, loaded_latency and c2c_latency modes. </s> |
<s>[INST] what is the -C flag [/INST] Specify the window size in KB for cache-to-cache transfer latency (default is 2,000 KB). This option is valid only in c2c_latency mode. </s> |
<s>[INST] what is the -d flag [/INST] Specify load injection delay. This option selects the number of cycles of delay that will be injected between bursts of memory accesses to throttle the b/w generated. When this option is not specified, once every few seconds (as specified by –t option) this value will be automatica... |
<s>[INST] what is the -D flag [/INST] Specify a maximum value for the random numbers that will be used in generating accesses in latency thread. For example, if a value of 8192 is specified, random numbers in the range of 1-8192 will be used. The randomization is not done over the entire buffer (-b size) to minimize th... |
<s>[INST] what is the -e flag [/INST] Do not modify the h/w prefetcher settings. H/W prefetcher settings are left unmodified. If this option is not specified, the tool will automatically change the prefetcher settings appropriately for various measurements. This option is valid in all modes. </s> |
<s>[INST] what is the -E flag [/INST] read extra n KB lines in writer thread in c2c_latency (default=0). This is used to force the lines out of either L1 or L2 into lower level caches (like L3). This option is valid only for c2c_latency mode. </s> |
<s>[INST] what is the -g flag [/INST] Specify the input file name with delays to inject for measuring latencies under different load levels. This file can specify many inject-delay values (one per line). If this option is not specified, a default list of values that are hard coded into the program is used. The default ... |
<s>[INST] what is the -G flag [/INST] Specify the buffer size in kB for extra reads in reader thread in c2c_latency mode </s> |
<s>[INST] what is the -h flag [/INST] Allocate buffers using 1GB huge pages. On Linux, you need to allocate 1GB pages with /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages </s> |
<s>[INST] what is the -H flag [/INST] Measure clean line hit latency in c2c_latency mode. Without this flag, the default setting measures Hit-modified latency. </s> |
<s>[INST] what is the -i flag [/INST] Select on which CPU the requested memory will reside for the latency measuring thread. It identifies the logical CPU that will allocate the memory and initialize it. The thread that is allocating the memory will pin itself to this CPU, allocate the memory and do a first ‘touch’ of... |
<s>[INST] what is the -I flag [/INST] Enable data integrity check. For 100% read traffic, checksum is calculated (basically, XOR is done at 8-byte granularity over the entire buffer on first read and checked against on all subsequent reads) and reported if there is any mismatch. When mismatch occurs, the program will e... |
<s>[INST] what is the -j flag [/INST] Allocate memory from the specified numa node. If this option is selected, -J or –i parameter should not be selected. This option is valid in idle_latency and loaded_latency modes. </s> |
<s>[INST] what is the -J flag [/INST] Specify a directory in which files for mmap will be created. This option relies on using file system mounted on persistent memory. This option is valid only in idle_latency mode. </s> |
<s>[INST] what is the -k flag [/INST] Specify a list of cpu numbers to be used for measurements. The cpu# can be a range separated by a hyphen, for example, “-k4-8” means logical cpu#s 4,5,6,7,8 are to be used. Comma separation is also supported, for example, “-k4-8,12-16,18” means cpus 4,5,6,7,8,12,13,14,15,16,18 are ... |
<s>[INST] what is the -K flag [/INST] Specify finer control over whether all 64 bytes of a cache line are accessed during loads/stores. Typically, more instructions need to be executed to access all the bytes of a cache line. For example, to load a 64B line, you need to execute 4 SSE instructions where each instruction... |
<s>[INST] what is the -l flag [/INST] Set the stride size in bytes. Default is 64 bytes. This option is valid in all modes except c2c_latency. </s> |
<s>[INST] what is the -L flag [/INST] Allocate the buffer using the hugetlbfs interface. In case of Windows o/s, large pages should be enabled appropriately. The system should have already reserved enough 2MB pages to satisfy the allocation request. This option is valid in all modes except c2c_latency. </s> |
<s>[INST] what is the -m flag [/INST] Specify the mask value (in hex) of CPUs to run the bandwidth generation threads. Only either –k or –m can be used and not both. CPU 0 should be excluded from this mask as it is used to run the latency measuring thread. If Intel® Hyper-Threading Technology is enabled, the other CPU ... |
<s>[INST] what is the -M flag [/INST] By default, MLC initializes buffers by writing increasing integer numbers to each line. If there is a need to initialize the buffers/memory with specific patterns, this option can be used. A pattern input file can be provided that has an entire cache line in hex form. There can be ... |
<s>[INST] what is the -n flag [/INST] Specify the maximum random number to be used in random access bandwidth generation. This option is valid only if specified along with –U option. For example, if a value of 8192 is specified, random numbers in the range of 1-8192 will be used. The randomization is not done over the ... |
<s>[INST] what is the -p flag [/INST] Specify a core number on each socket (in the form of comma separated CPU numbers) where a dummy thread is executed to keep that CPU 100% active. The dummy thread executes yield() system call in a loop. Since current generation processors support aggressive power management, sockets... |
<s>[INST] what is the -P flag [/INST] Execute CLFLUSHOPT instruction after any stores to addresses in persistent memory region. If stores are not flushed immediately, they may be evicted from the last level cache in any order and that may not provide the most optimal b/w. When this option is specified, each store is fo... |
<s>[INST] what is the -Q flag [/INST] Execute CLFLUSHOPT instruction after any stores to any addresses. This option is similar to the previous option (-P) but applies to all address range and not persistent memory range only. This option is valid only in AVX512 mode which requires the specification of –Z option as well... |
<s>[INST] what is the -r flag [/INST] Initialize the buffer (used by latency thread) with pseudo-random values so the access pattern to memory will be random for latency measurement. For random access in loadgeneration threads, use option –U. This option is valid in idle_latency, latency_matrix and loaded_latency modes... |
<s>[INST] what is the -R flag [/INST] Select 100% read traffic. If this option is specified –W should not be used. This option is valid in bandwidth_matrix and loaded_latency modes. </s> |
<s>[INST] what is the -S flag [/INST] Specify the cpu id to pin the 3rd thread in cache-to-cache transfer latency measurement. Please see example 8.8.4. This option is valid only in c2c_latency mode </s> |
<s>[INST] what is the -t flag [/INST] Set time in seconds during which each measurement is captured. Default is 2 seconds. This option is valid in all modes except c2c_latency </s> |
<s>[INST] what is the -T flag [/INST] Specify this flag if only b/w is desired without latency values. If this is selected, then the –m option can have a mask value covering all available CPUs including 0. Similarly, if –k is specified, it can include cpu# 0 in the cpu range. This option is valid only in loaded_latency... |
<s>[INST] what is the -u flag [/INST] Specify this flag when L3 cache b/w measurement is needed. With this flag, each b/w generation thread shares the same buffer and does not allocate its own. Due to shared data, there is no write-back of clean lines from L2 to L3 thus allowing only real read traffic from L3 to be mea... |
<s>[INST] what is the -U flag [/INST] Specify this flag to enable random access for bandwidth generation threads (default: off, only sequential access). This means that the threads generating the traffic that are used for bandwidth measurements access memory with “randomness” – i.e. they do not sequentially stride thro... |
<s>[INST] what is the -v flag [/INST] Specify this flag to print the verbose output: additional details about what MLC is doing behind the scenes. This is useful for debugging. This option is valid in all modes. </s> |
<s>[INST] what is the -w flag [/INST] Specify the cpu id to pin hit/hitm writer thread. This option is valid only in c2c_latency mode. </s> |
<s>[INST] what is the -W flag [/INST] Specify read to write ratio for the b/w generation thread in bandwidth_matrix and loaded_latency modes . –Wn where n can take the following values (reads and writes are as observed on the memory controller): The last 3 values (21, 23 and 27) can only be specified in the per-thread-... |
<s>[INST] what is the -x flag [/INST] Set the number of iterations in millions. If this option is specified, then –t should not be specified. A value of 0 (-x0) will perform only one iteration over the buffer allocated. This option is valid in idle_latency, latency_matrix and loaded_latency modes. </s> |
<s>[INST] what is the -X flag [/INST] Specify this flag to use only 1 hyper-thread per core for bandwidth measurements. When this flag is specified, MLC picks the first hyper-thread id out of all the hyperthreads of each core to run the bandwidth thread. The other hyperthread(s) of the cores will not be used to run any... |
<s>[INST] what is the -Y flag [/INST] Specify this flag to use AVX2 load and store instructions for generating the traffic. This option is valid in bandwidth_matrix, max_bandwidth, peak_injection_bandwidth and loaded_latency modes only. By default, only SSE2 (128-bit loads/stores) instructions are used. </s> |
<s>[INST] what is the -Z flag [/INST] Specify this flag to use AVX-512 load and store instructions for generating the traffic. This option is valid in bandwidth_matrix, max_bandwidth, peak_injection_bandwidth and loaded_latency modes only. By default, only SSE2 (128-bit loads/stores) instructions are used. </s> |
<s>[INST] how to measure idle latency and what are the flags used with it? [/INST] To measure idle latency the command line is ./mlc --idle_latency. The following flags go with idle latency measurements [-a] [-bn] [-cn] [-Dn] [-e] [-in] [-jn] [-Jn] [-ln] [-L|-h] [-r] [-tn] [-xn] [-X] </s> |
<s>[INST] how to measure max bandwidth and what are the flags that goes with it? [/INST] To measure max bandwidth the command line is ./mlc --max_bandwidth. The flags that are used with it are [-bn] [-e] [-kn|-mn] [-ln] [-L|-h] [-M<filename>] [-tn] [-X] [-Y] [-Z] </s> |
<s>[INST] how to measure the latency matrix and what are the flags used with it? [/INST] To measure latency matrix the command line is ./mlc --latency_matrix. The falgs that are used with it are [-a] [-bn] [-Dn] [-e] [-ln] [-L|-h] [-tn] [-r] [-tn] [-xn] [-X] </s> |
<s>[INST] how to measure the bandwidth matrix and what are the flags used with it? [/INST] to measure bandwidth matrix the command line is ./mlc --bandwidth_matrix. The flags that are used with it are [-bn] [-e] [-ln] [-L|-h] [-M<filename>] [-R] [-tn] [-Wn] [-X] [-Y] [-Z] </s> |
<s>[INST] how to measure the peak injection bandwidth and what are the flags that goes with it? [/INST] to measure peak injection bandwidth the command line is ./mlc --peak_injection_bandwidth. The flags that go with it are [-bn] [-e] [-kn|-mn] [-ln] [-L|-h] [-M<filename>] [-tn] [-X] [-Y] [-Z] </s> |
<s>[INST] how to measure the loaded latency and what are the flags that goes with it? [/INST] to measure loaded latency the command line is ./mlc --loaded_latency. the flags that goes with it are [-bn] [-B] [-cn] [-dn] [-Dn] [-e] [-g<filename>] [-in] [-I] [-jn] [-kn|-mn] [-Kn] [-ln] [-L|-h] [-M<filename>] [-nn] [-o<fil... |
<s>[INST] how to measure cache to cache latency and what are the flags that goes with it. [/INST] to measure the cache to cache latency the command line is --c2c_latency and the flags that goes with it are [-bn] [-cn] [-Cn] [-Dn] {-En] [-Gn] [-H] [-in] [-L|-h] [-r] [-Sn] [-wn] [-xn] </s> |
<s>[INST] run default mlc test [/INST] ./mlc </s> |
<s>[INST] run mlc without modifying the hardware prefetchers [/INST] ./mlc -e </s> |
<s>[INST] measure idle latency [/INST] ./mlc --idle_latency </s> |
<s>[INST] measure latency matrix [/INST] ./mlc --latency_matrix </s> |
<s>[INST] measure bandwidth matrix [/INST] ./mlc --bandwidth_matrix </s> |
<s>[INST] measure peak injection bandwidth [/INST] ./mlc -peak_injection_bandwidth </s> |
<s>[INST] measure maximum bandwidth [/INST] ./mlc --max_bandwidth </s> |
<s>[INST] meausre loaded latency [/INST] ./mlc --loaded_latency </s> |
<s>[INST] measure c2c latency [/INST] ./mlc --c2c_latency </s> |
<s>[INST] Measuring local memory idle latency from a specific CPU [/INST] ./mlc --idle_latency –c4 –i4 </s> |
<s>[INST] Measuring remote memory idle latency from a specific CPU [/INST] ./mlc --idle_latency –c0 –i8 </s> |
<s>[INST] Measuring idle latencies with different stride length [/INST] ./mlc --idle_latency –c4 –i4 –l256 </s> |
<s>[INST] Measuring cache hit idle latency [/INST] ./mlc --idle_latency –b3000 –c0 –t3 </s> |
<s>[INST] Measuring idle latencies using fixed number of requests [/INST] ./mlc --idle_latency –x10 </s> |
<s>[INST] Measuring idle latency to a specific NUMA node [/INST] ./mlc --idle_latency –c0 –j3 </s> |
<s>[INST] Measuring idle latency with random access [/INST] mlc --idle_latency –c0 –r –D8192 </s> |
<s>[INST] Measuring latencies on all the cpus [/INST] ./mlc --latency_matrix –a </s> |
<s>[INST] Measuring b/w matrix with 100% reads and no writes [/INST] ./mlc --bandwidth_matrix –R </s> |
<s>[INST] Measuring b/w matrix with 2 reads and 1 writes [/INST] ./mlc --bandwidth_matrix –W2 </s> |
<s>[INST] Measuring b/w matrix with 3 reads and 1 writes [/INST] ./mlc --bandwidth_matrix –W3 </s> |
<s>[INST] Measuring b/w matrix with 1 read and 1 writes [/INST] ./mlc --bandwidth_matrix –W5 </s> |
<s>[INST] Measuring b/w matrix with no reads and 100% non-temporal writes [/INST] ./mlc --bandwidth_matrix –W6 </s> |
<s>[INST] Measuring b/w matrix with 2 reads and 1 non-temporal write [/INST] ./mlc --bandwidth_matrix –W7 </s> |
<s>[INST] Measuring b/w matrix with 3 reads and 1 non-temporal write [/INST] ./mlc --bandwidth_matrix –W9 </s> |
<s>[INST] Measuring b/w matrix with 1 reads and 1 non-temporal write [/INST] ./mlc --bandwidth_matrix –W8 </s> |
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