Hi, On Fri, Nov 09, 2018 at 09:22:42AM +0100, Jiri Olsa wrote: > On Tue, Nov 06, 2018 at 11:53:02AM +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 [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 > > FYI I was rebasing my threads branch on top of this and > first 2 won't apply anymore on Arnaldo's perf/core > > Arnaldo, > could we get this merged soon? the world around is moving > fast and we don't want 20th revision on this ;-)
I think I gave my ack to this already too. Thanks, Namhyung
