perf + Flame Graph火焰圖分析程序性能

1、perf命令簡要介紹

性能調優時，我們通常需要分析查找到程序百分比高的熱點代碼片段，這便需要使用 perf record 記錄單個函數級別的統計信息，並使用 perf report 來顯示統計結果；

usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

 The most commonly used perf commands are:
   annotate        Read perf.data (created by perf record) and display annotated code
   archive         Create archive with object files with build-ids found in perf.data file
   bench           General framework for benchmark suites
   buildid-cache   Manage build-id cache.
   buildid-list    List the buildids in a perf.data file
   data            Data file related processing
   diff            Read perf.data files and display the differential profile
   evlist          List the event names in a perf.data file
   inject          Filter to augment the events stream with additional information
   kmem            Tool to trace/measure kernel memory properties
   kvm             Tool to trace/measure kvm guest os
   list            List all symbolic event types
   lock            Analyze lock events
   mem             Profile memory accesses
   record          Run a command and record its profile into perf.data
   report          Read perf.data (created by perf record) and display the profile
   sched           Tool to trace/measure scheduler properties (latencies)
   script          Read perf.data (created by perf record) and display trace output
   stat            Run a command and gather performance counter statistics
   test            Runs sanity tests.
   timechart       Tool to visualize total system behavior during a workload
   top             System profiling tool.
   trace           strace inspired tool
   probe           Define new dynamic tracepoints

 See 'perf help COMMAND' for more information on a specific command.

舉例

perf record -e cpu-clock -g -p 222

-g 選項是告訴perf record額外記錄函數的調用關系

-e cpu-clock 指perf record監控的指標為cpu周期

-p 指定需要record的進程pid

 

程序運行完之后，perf record會生成一個名為perf.data的文件，如果之前已有，那么之前的perf.data文件會被覆蓋

獲得這個perf.data文件之后，就需要perf report工具進行查看

perf report -i perf.data

-i 指定要查看的文件

 以診斷fluentd為例,report結果：

$perf report  -i perf.data

這種格式很不直觀

 2、使用火焰圖展示結果

1、Flame Graph項目位於GitHub上：https://github.com/brendangregg/FlameGraph

2、可以用git將其clone下來：git clone https://github.com/brendangregg/FlameGraph.git

 注意：git clone之后，下面用到的*.pl文件先給+x可執行權限，注意路徑

我們以perf為例，看一下flamegraph的使用方法：

1、第一步

$perf record -e cpu-clock -g -p 28591

Ctrl+c結束執行后，在當前目錄下會生成采樣數據perf.data.

2、第二步

用perf script工具對perf.data進行解析

perf script -i perf.data &> perf.unfold

3、第三步

將perf.unfold中的符號進行折疊：

./stackcollapse-perf.pl perf.unfold &> perf.folded

注意：該命令可能有錯誤，錯誤提示在perf.folded

4、最后生成svg圖：

./flamegraph.pl perf.folded > perf.svg