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... [jolsa@krava 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
