Introduction

Codes & slides for the presentation done to the 24th performance user group at Paris the 17/09/2015.

Slides

I recommand looking at the presentation first before playing with commands below.

Notes

Example - Calculus on simple matrix

    cd src/02-matrix
    make build
    time valgrind --tool=callgrind --simulate-cache=yes --dump-instr=yes --collect-jumps=yes ./app 100 100

Look at symbol table

    cd src/00-empty
    make build
    readelf -s ./app;
    readelf -s /lib/x86_64-linux-gnu/libc.so.6 | grep malloc

    # Strip effect on the symbol table
    strip ./app
    readelf -s ./app;

Profiling Callgrind

    cd src/02-matrix
    make build

    # Profiling with callgrind for 100 * 100 matrix
    time valgrind --tool=callgrind --simulate-cache=yes --dump-instr=yes --collect-jumps=yes ./app 100 100

    # Perf impact of callgrind
    time ./app 100 100

Thread dump on Native application - Gstack

    cd ~/sources/memcached

    sudo -s

Bash function to generate thread dump for native application as you can do with jstack

    gstack() {
      tmp=$(tempfile)
      echo thread apply all bt >"$tmp"
      gdb -batch -nx -q -x "$tmp" -p "$1"
      rm -f "$tmp"
    }

Use it

    ./memcached &

    while sleep 1; do gstack @pid@ ; done

Perf - Some commands

Get a list of avaible counters.

perf list

Get an overview of counters for an application

perf stat ./app

Perf - Impact on performance

    time ./app 500 500
    time perf record -g ./app 500 500

Memcached - Symbol table

    cd ~/sources/memcached
    readelf -s ./memcached

Generate flamegraph from gdb stacktraces

    cd ~/sources/memcached
    ./memcached &

    php src/03-memcache-php/memcache-set.php

    while sleep 0.1; do gstack 8748; done > stack.txt
    cat stack.txt | stackcollapse-gdb.pl | flamegraph.pl > gdb_graph.svg

MEMCACHE - PROFILING WITH PERF

    cd ~/sources/memcached

    perf record -g ./memcached

    php src/03-memcache-php/memcache-set.php
    perf report

    Warning to /proc/sys/kernel/kptr_restrict

MEMCACHED - PROFILING CPU CYCLE WITH PERF - WITH KERNEL STACKTRACE

    ./memcached &
    sudo perf record -a -g -p @pid@

    php src/03-memcache-php/memcache-set.php
    perf report