如何使用Linux性能工具进行代码理解

Question

I'm fascinated by the ability of 'perf' to record call graphs and am trying to understand how to use it to understand a new code base.

I compiled the code in debug mode, and ran unit tests using the following command:

perf record --call-graph dwarf make test

This creates a 230 meg perf.data. I then write out the call graph

perf report --call-graph --stdio > callgraph.txt

This creates a 50 meg file.

Ideally, I would only like to see code belonging to the project, not kernel code, system calls, c++ standard libraries, even boost and whatever other third party software. Currently I see items like __GI___dl_iterate_phdr, _Unwind_Find_FDE, etc.

I love the flamegraph project. However, that visualization isn't good for code comprehension. Are there any other projects, write-ups, ideas, which might be helpful?

Answer 1

perf report -g for huge application should not be dumped to external file as too verbose. Collected perf.data (with -g ) will work without file redirection with interactive perf report TUI interface. You may disable callgraph reporting to find functions took most time with perf record without -g or perf report --no-children .

There is gprof2dot script ( https://github.com/jrfonseca/gprof2dot ) to visualize lagre perf report call-graphs as compact picture (graph).

There is also Brendan D. Gregg's interactive FlameGraphs in svg/js; and he often notes in presentations that perf report -g output shows many megabyte raw dumps of report as lot of A4 pages. There is usage instruction for the perf: http://www.brendangregg.com/FlameGraphs/cpuflamegraphs.html#perf :

# git clone https://github.com/brendangregg/FlameGraph  # or download it from github
# cd FlameGraph
# perf record -F 99 -g -- ../command
# perf script | ./stackcollapse-perf.pl > out.perf-folded
# ./flamegraph.pl out.perf-folded > perf-kernel.svg

PS: Why you are profiling make process? Try to select some test and profile only them. Use lower profile frequency to get smaller perf.data file. Also disable kernel-mode samples with :u suffix of default event "cycles": perf record -F 99 -g -e cycles:u -- ../command