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    SubjectRe: [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads
    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

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