Messages in this thread | | | Date | Mon, 15 Oct 2018 12:17:48 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH v14 0/3]: perf: reduce data loss when profiling highly parallel CPU bound workloads |
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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>
thanks, jirka
> > 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 [1] lowers > data loss metrics value providing 2x improvement (from 98% to ~1%) > > Asynchronous trace streaming is currently limited to glibc linkage. > musl libc [5] also provides Posix AIO API implementation, however > the patchkit is not tested with it. There may be other libc libraries > linked by Perf tool that currently lack Posix AIO API support [2], > [3], [4] so NO_AIO define may be used to limit Perf tool binary to > serial streaming only. > > --- > Alexey Budankov (3): > perf util: map data buffer for preserving collected data > perf record: enable asynchronous trace writing > perf record: extend trace writing to multi AIO > > tools/perf/Documentation/perf-record.txt | 5 + > tools/perf/Makefile.config | 5 + > tools/perf/Makefile.perf | 7 +- > tools/perf/builtin-record.c | 252 ++++++++++++++++++++++++++++++- > tools/perf/perf.h | 1 + > tools/perf/util/evlist.c | 6 +- > tools/perf/util/evlist.h | 2 +- > tools/perf/util/mmap.c | 146 +++++++++++++++++- > tools/perf/util/mmap.h | 26 +++- > 9 files changed, 439 insertions(+), 11 deletions(-) > > --- > Changes in v14: > - implement default nr_cblocks_default variable > - fix --aio option handling > Changes in v13: > - named new functions with _aio_ word > - grouped aio functions under single #ifdef HAVE_AIO_SUPPORT > - moved perf_mmap__aio_push() stub into header > - removed trailed white space > Changes in v12: > - applied stub functions design for the whole patch kit > - grouped AIO related data into a struct under struct perf_mmap > - implemented record__aio_get/set_pos(), record__aio_enabled() > - implemented simple --aio option > - extended --aio option to --aio-cblocks=<n> > Changes in v11: > - replacing the both lseek() syscalls in every loop iteration by the only > two syscalls just before and after the loop at record__mmap_read_evlist() > and advancing *in-flight* off file pos value at perf_mmap__aio_push() > Changes in v10: > - moved specific code to perf_mmap__aio_mmap(), perf_mmap__aio_munmap(); > - adjusted error reporting by using %m > - avoided lseek() setting file pos back in case of record__aio_write() failure > - compacted code selecting between serial and AIO streaming > - optimized call places of record__mmap_read_sync() > - added description of aio-cblocks option into perf-record.txt > Changes in v9: > - enable AIO streaming only when --aio-cblocks option is specified explicitly > - enable AIO based implementation when linking with glibc only > - define NO_AIO to limit Perf binary to serial implementation > Changes in v8: > - run the whole thing thru checkpatch.pl and corrected found issues except > lines longer than 80 symbols > - corrected comments alignment and formatting > - moved multi AIO implementation into 3rd patch in the series > - implemented explicit cblocks array allocation > - split AIO completion check into separate record__aio_complete() > - set nr_cblocks default to 1 and max allowed value to 4 > Changes in v7: > - implemented handling record.aio setting from perfconfig file > Changes in v6: > - adjusted setting of priorities for cblocks; > - handled errno == EAGAIN case from aio_write() return; > Changes in v5: > - resolved livelock on perf record -e intel_pt// -- dd if=/dev/zero of=/dev/null count=100000 > - data loss metrics decreased from 25% to 2x in trialed configuration; > - reshaped layout of data structures; > - implemented --aio option; > - avoided nanosleep() prior calling aio_suspend(); > - switched to per-cpu aio multi buffer record__aio_sync(); > - record_mmap_read_sync() now does global sync just before > switching trace file or collection stop; > Changes in v4: > - converted mmap()/munmap() to malloc()/free() for mmap->data buffer management > - converted void *bf to struct perf_mmap *md in signatures > - written comment in perf_mmap__push() just before perf_mmap__get(); > - written comment in record__mmap_read_sync() on possible restarting > of aio_write() operation and releasing perf_mmap object after all; > - added perf_mmap__put() for the cases of failed aio_write(); > Changes in v3: > - written comments about nanosleep(0.5ms) call prior aio_suspend() > to cope with intrusiveness of its implementation in glibc; > - written comments about rationale behind coping profiling data > into mmap->data buffer; > Changes in v2: > - converted zalloc() to calloc() for allocation of mmap_aio array, > - cleared typo and adjusted fallback branch code; > > --- > > [1] http://man7.org/linux/man-pages/man7/aio.7.html > [2] https://android.googlesource.com/platform/bionic/+/master/docs/status.md > [3] https://www.uclibc.org/ > [4] https://uclibc-ng.org/ > [5] https://www.musl-libc.org/
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