Re: [mpg123-devel] Unusual CPU usage

[Thomas O. <tho...@or...>]

Am Thu, 5 Jan 2012 19:34:06 +0000
schrieb Clive Cooper <cl...@wi...>: 

> I would appreciate some help with a command line for use with perf.

Yeah, I had a hard time with that, too. For a start, try

	perf record $mpg123_command

then

	perf report

This writes the profiling data into the current directory. One can achieve different views with parameter to record / report. On my system, `perf report` opens a TUI interface on a the terminal, but gives plain text when piping the output. Example:

shell$ perf record mpg123 -t something.mp3
...
shell$ perf report | cat
# Events: 715  cycles
#
# Overhead  Command        Shared Object                           Symbol
# ........  .......  ...................  ...............................
#
    41.69%   mpg123  libmpg123.so.0.29.6  [.] III_dequantize_sample
    24.54%    :6136         2b61410cc624  [.]     2b61410cc624
     7.70%   mpg123  libmpg123.so.0.29.6  [.] INT123_dct64_x86_64
     7.23%   mpg123  libmpg123.so.0.29.6  [.] INT123_dct36
     5.17%   mpg123  libmpg123.so.0.29.6  [.] INT123_do_layer3
     4.88%   mpg123  libmpg123.so.0.29.6  [.] Loop_start_1
     3.80%   mpg123  libmpg123.so.0.29.6  [.] Loop_start_2
     0.85%   mpg123  [kernel.kallsyms]    [k] copy_page_c
     0.68%   mpg123  libmpg123.so.0.29.6  [.] III_get_scale_factors_1.isra.1
     0.54%   mpg123  libmpg123.so.0.29.6  [.] INT123_synth_1to1_stereo_x86_64
     0.54%    :6136  [kernel.kallsyms]    [k] copy_user_generic_string
     0.41%    :6136  [kernel.kallsyms]    [k] generic_file_aio_read
     0.27%   mpg123  libmpg123.so.0.29.6  [.] dct12
     0.27%    :6136  [kernel.kallsyms]    [k] acpi_os_read_port
     0.18%    :6136  [kernel.kallsyms]    [k] read_hpet
     0.14%    :6136  [kernel.kallsyms]    [k] intel_pmu_disable_all
     0.14%   mpg123  [kernel.kallsyms]    [k] file_read_actor
     0.14%    :6136  [kernel.kallsyms]    [k] fget_light
     0.14%   mpg123  libmpg123.so.0.29.6  [.] decode_header.part.2
     0.14%   mpg123  mpg123               [.] play_frame
     0.14%   mpg123  libmpg123.so.0.29.6  [.] mpg123_decode_frame
     0.14%   mpg123  [kernel.kallsyms]    [k] system_call
     0.14%    :6136  [kernel.kallsyms]    [k] swiotlb_map_sg_attrs
     0.13%   mpg123  [kernel.kallsyms]    [k] __rcu_read_lock
     0.01%   mpg123  [kernel.kallsyms]    [k] __memcpy
     0.00%    :6136  [kernel.kallsyms]    [k] intel_pmu_enable_all


#
# (For a higher level overview, try: perf report --sort comm,dso)
#

This is not totally conclusive (you have to guess what 2b61410cc624 is, I'd try the asm code for synth_1to1), but in your case with high ALSA usage, something else than III_dequantize_sample should be on the top.


Alrighty then,

Thomas.