From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
Andi Kleen <ak@linux.intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads
Date: Thu, 25 Oct 2018 08:12:37 -0300 [thread overview]
Message-ID: <20181025111237.GA3782@kernel.org> (raw)
In-Reply-To: <20181025085439.GA4722@krava>
Em Thu, Oct 25, 2018 at 10:54:39AM +0200, Jiri Olsa escreveu:
> On Thu, Oct 25, 2018 at 10:59:36AM +0300, Alexey Budankov wrote:
> > Hi,
> >
> > On 15.10.2018 13:17, Jiri Olsa wrote:
> > > On Mon, Oct 15, 2018 at 09:26:09AM +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
> > >
> > > I ran above on 24 cpu server and could not see the gain,
> > > but I guess I'd need much bigger server to see that
> > >
> > > anyway, the code is now nicely separated, and given the
> > > advertised results below I have no objections
> > >
> > > Reviewed-by: Jiri Olsa <jolsa@kernel.org>
> >
> > Is the plan Jiri mentioned earlier to have it as a stand alone patch kit
> > or upstream the changes into mainline?
>
> I haven't heard from Arnaldo yet, but I'd like to have this merged in
I'll try and go over it today.
- Arnaldo
prev parent reply other threads:[~2018-10-25 11:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 6:26 [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads Alexey Budankov
2018-10-15 6:42 ` [PATCH v14 1/3]: perf util: map data buffer for preserving collected data Alexey Budankov
2018-11-01 18:47 ` Song Liu
2018-11-02 16:14 ` Alexey Budankov
2018-10-15 6:44 ` [PATCH v14 2/3]: perf record: enable asynchronous trace writing Alexey Budankov
2018-11-01 18:42 ` Song Liu
2018-11-02 16:11 ` Alexey Budankov
2018-10-15 6:46 ` [PATCH v14 3/3]: perf record: extend trace writing to multi AIO Alexey Budankov
2018-11-01 18:30 ` Song Liu
2018-11-02 16:12 ` Alexey Budankov
2018-10-15 10:17 ` [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads Jiri Olsa
2018-10-25 7:59 ` Alexey Budankov
2018-10-25 8:54 ` Jiri Olsa
2018-10-25 11:12 ` Arnaldo Carvalho de Melo [this message]
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