Messages in this thread | | | Date | Thu, 25 Oct 2018 08:12:37 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads |
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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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