Perf simple process for multithreaded profile

Background knowledge

Perf It is a tool for software performance analysis , adopt Perf, Applications can take advantage of PMU,tracepoint And special counters in the kernel for performance statistics .Perf It can not only analyze the performance problems of applications (per thread), You can also analyze the performance problems of the kernel , Handle all performance related events ： Hardware events during program operation , Such as instructions retired ,processor clock cycles etc. ; Software events , Such as Page Fault And process switching .

Perf The basic principle is to sample the monitored object , The simplest case is based on tick Interrupt sampling , That is to say tick Trigger sampling point in interrupt , Determine the current context of the program at the sampling point . Suppose a program 90% All the time spent on the function func1() On , that 90% All of the sampling points should fall in the function func1() In the context of , The longer the sampling time is , The more reliable the above inference is . Use perf Have administrator privileges

Use perf Multithreading profile

Prepare multithreaded program

In this program , Two threads were created . Ran different times func1() Method .gcc -lpthread main.c

#include <pthread.h>
#include <stdio.h>
#include <string.h>

pthread_t thread[2];

void func1() {
    
    int i = 0;
    while (i<10000)
        ++i;
}

void func2() {
    
    int i = 0;

    while (i<10000)
        i = i*2;
    func1();
}

void *thread1()
{
    
        for (;;)
        {
    
            func1();
        }

        pthread_exit(NULL);
}

void *thread2()
{
    
        for (;;)
        {
    
            func2();
        }

        pthread_exit(NULL);
}

void thread_create(void)
{
    
        int temp;
        memset(&thread, 0, sizeof(thread));
        if((temp = pthread_create(&thread[0], NULL, thread1, NULL)) != 0)
                printf(" Threads 1 Create failure !\n");
        else
                printf(" Threads 1 Be created \n");

        if((temp = pthread_create(&thread[1], NULL, thread2, NULL)) != 0)
                printf(" Threads 2 Create failure \n");
        else
                printf(" Threads 2 Be created \n");
}


int main()
{
    
        thread_create();
        pthread_join(thread[0],NULL);
        printf(" Threads 1 Join in ");
        pthread_join(thread[1],NULL);
        printf(" Threads 2 Join in ");

        return 0;
}

Use perf Sample the program

For the program that hasn't been started

[email protected]:/home/banfushen/perf_cpu/multi_thread# perf record -h
Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    ...
    -F, --freq <n>        profile at this frequency
    -g                    enables call-graph recording
    -p, --pid <pid>       record events on existing process id
    -t, --tid <tid>       record events on existing thread id
    ...

perf record -g -F 99 ./a.out, Sampling multithreaded programs , sampling frequency 99,(-F 99: sample at 99 Hertz (samples per second). I’ll sometimes sample faster than this (up to 999 Hertz), but that also costs overhead. 99 Hertz should be negligible. Also, the value ‘99’ and not ‘100’ is to avoid lockstep sampling, which can produce skewed results.). After running, you will get a perf.data, To get the flame diagram , Other tools are needed .

For the program that has been started

For programs that have been started , To get pid,perf record -g -F 99 -p <pid>

Download tool FlameGraph

git clone https://github.com/brendangregg/FlameGraph.git

[email protected]:~/perf_cpu/FlameGraph$ pwd
/home/banfushen/perf_cpu/FlameGraph

Generate flame chart

Yes perf.data Generate flame chart ( According to the above, it is a process )

perf script |/home/banfushen/perf_cpu/FlameGraph/stackcollapse-perf.pl|/home/banfushen/perf_cpu/FlameGraph/flamegraph.pl > output.svg

Generate a flame diagram for a single thread

You know, threads id

[email protected]:/home/banfushen/perf_cpu/multi_thread# perf script -h

 Usage: perf script [<options>]
    or: perf script [<options>] record <script> [<record-options>] <command>
    or: perf script [<options>] report <script> [script-args]
    or: perf script [<options>] <script> [<record-options>] <command>
    or: perf script [<options>] <top-script> [script-args]

    ...
    -v, --verbose         be more verbose (show symbol address, etc)
        --pid <pid[,pid...]>
        --tid <tid[,tid...]>
                          only consider symbols in these tids

perf script -v --tid <tid> Specified thread
perf script -v --tid 2283471|/home/banfushen/perf_cpu/FlameGraph/stackcollapse-perf.pl|/home/banfushen/perf_cpu/FlameGraph/flamegraph.pl > output1.svg

Generate a flame diagram for multiple threads

perf script -v --tid <tid[,tid...]> Specify multiple threads
perf script -v --tid 2283472,2283471|/home/banfushen/perf_cpu/FlameGraph/stackcollapse-perf.pl|/home/banfushen/perf_cpu/FlameGraph/flamegraph.pl > output3.svg

Reference material :
perf Examples
perf Performance analysis
Performance analysis tool perf elementary analysis
utilize perf analyse Linux Applications
Linux Performance analysis tool Perf brief introduction