linux-kernel - Re: [PATCH v7 0/2]: perf: reduce data loss when profiling highly parallel CPU bound workloads

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Message-ID: <34e2f944-f5f3-094a-5997-899cea92d206@linux.intel.com>
Date:   Wed, 5 Sep 2018 20:37:32 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 0/2]: perf: reduce data loss when profiling highly
 parallel CPU bound workloads

Hi,

On 05.09.2018 14:28, Jiri Olsa wrote:
> On Wed, Sep 05, 2018 at 10:16:42AM +0300, Alexey Budankov wrote:
>>
>> Currently in record mode the tool implements trace writing serially. 
>> The algorithm loops over mapped per-cpu data buffers and stores 
>> ready data chunks into a trace file using write() system call.
>>
>> At some circumstances the kernel may lack free space in a buffer 
>> because the other buffer's half is not yet written to disk due to 
>> some other buffer's data writing by the tool at the moment.
>>
>> Thus serial trace writing implementation may cause the kernel 
>> to loose profiling data and that is what observed when profiling 
>> highly parallel CPU bound workloads on machines with big number 
>> of cores.
>>
>> Experiment with profiling matrix multiplication code executing 128 
>> threads on Intel Xeon Phi (KNM) with 272 cores, like below,
>> demonstrates data loss metrics value of 98%:
>>
>> /usr/bin/time perf record -o /tmp/perf-ser.data -a -N -B -T -R -g \
>>     --call-graph dwarf,1024 --user-regs=IP,SP,BP \
>>     --switch-events -e cycles,instructions,ref-cycles,software/period=1,name=cs,config=0x3/Duk -- \
>>     matrix.gcc
>>
>> Data loss metrics is the ratio lost_time/elapsed_time where 
>> lost_time is the sum of time intervals containing PERF_RECORD_LOST 
>> records and elapsed_time is the elapsed application run time 
>> under profiling.
>>
>> Applying asynchronous trace streaming thru Posix AIO API
>> (http://man7.org/linux/man-pages/man7/aio.7.html) 
>> lowers data loss metrics value providing 2x improvement -
>> lowering 98% loss to almost 0%.
>>
>> ---
>>  Alexey Budankov (2):
>>         perf util: map data buffer for preserving collected data
>> 	perf record: enable asynchronous trace writing
>>  
>>  tools/perf/builtin-record.c | 197 +++++++++++++++++++++++++++++++++++++++++++-
>>  tools/perf/perf.h           |   1 +
>>  tools/perf/util/evlist.c    |   7 +-
>>  tools/perf/util/evlist.h    |   3 +-
>>  tools/perf/util/mmap.c      | 110 +++++++++++++++++++++----
>>  tools/perf/util/mmap.h      |  10 ++-
>>  6 files changed, 302 insertions(+), 26 deletions(-)
>>
>> ---
>>  Changes in v7:
>>  - implemented handling record.aio setting from perfconfig file
> 
> can't apply this version on Arnaldo's perf/core...

my git remote -v

origin	git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip (fetch)
origin	git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip (push)

branch is perf/core, according to MAINTAINERS content.

What is Arnaldo's perf/core? This one?

git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux

and branch is perf/core?

> 
> [jolsa@...va linux-perf]$ git am /tmp/ab/
> Applying: perf util: map data buffer for preserving collected data
> error: patch failed: tools/perf/util/mmap.c:166
> error: tools/perf/util/mmap.c: patch does not apply
> 
> thanks,
> jirka
>