On Mon, Jun 15, 2020 at 1:32 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Sun, 14 Jun 2020 18:13:21 +0430 > ahmadkhorrami <ahmadkhorrami@xxxxxxxx> wrote: > > > Hi, > > > > I used the following command to sample backtraces for a simple "ffmpeg" > > benchmark: > > sudo perf record -d --call-graph dwarf,65528 -c 1000000 -e > > mem_load_uops_retired.l3_miss:u ffmpeg -i > > /media/ahmad/DATA/Videos/video.mp4 -threads 1 -vf spp out.mp4 > > > > As can be seen PEBS is not used, the stack size is set to the maximum > > and the sampling period is quite large. I also limited the thread count, > > but this is the first portion of "perf script --no-demangle" output: > > ffmpeg 11750 6670.061261: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeab68844 x264_pixel_avg_w16_avx2+0x4 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > > > ffmpeg 11750 6670.274835: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeab68844 x264_pixel_avg_w16_avx2+0x4 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > > > ffmpeg 11750 6670.496159: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeab8ef89 x264_pixel_sad_x4_16x16_avx2+0x49 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > > > ffmpeg 11750 6670.852598: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeaac97b3 pixel_memset+0x293 (inlined) > > 7fffeaac97b3 plane_expand_border+0x293 (inlined) > > 7fffeaac97b3 x264_frame_expand_border_filtered+0x293 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab463bc x264_fdec_filter_row+0x69c > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab49523 x264_slice_write+0x1873 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab85285 x264_stack_align+0x15 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab45bdb x264_slices_write+0xfb > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 5555561e3d87 [unknown] ([heap]) > > > > ffmpeg 11750 6671.110007: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeab6cdde x264_frame_init_lowres_core_avx2+0x8e > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > > > ffmpeg 11750 6671.463562: 1000000 mem_load_uops_retired.l3_miss:u: > > 0 5080021 N/A|SNP N/A|TLB N/A|LCK N/A > > 7fffeaabf806 x264_macroblock_load_pic_pointers+0x886 (inlined) > > 7fffeaabf806 x264_macroblock_cache_load+0x886 (inlined) > > 7fffeaabf806 x264_macroblock_cache_load_progressive+0x886 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab49204 x264_slice_write+0x1554 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab85285 x264_stack_align+0x15 > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 7fffeab45bdb x264_slices_write+0xfb > > (/usr/lib/x86_64-linux-gnu/libx264.so.152) > > 1c [unknown] ([unknown]) > > > > None of the backtraces are correct. Because none of them begin with > > "__start" or "__GI___clone". I also used "LBR", instead. But it has more > > size constraints and, therefore, not suitable. The important thing to > > note is that the problem occurs only with user space events (and for all > > events that I checked). I do not think that the problem is with > > DebugInfo. Because I manually used "perf_event_open()" system call > > (without using "Perf") and the problem was still there (with raw > > callstack IPs). > > > > Therefore, I assumed that the problem is inside the kernel. Precisely, > > it should be where the userspace callchain is extracted or dumped. I > > looked for the latter (i.e., the callchain dump implementation) and it > > seemed to be here: > > https://github.com/torvalds/linux/blob/master/kernel/events/core.c#L6786 > > > > But I could not (or, equivalently, did not know how to) view the user > > callchain instruction pointers. > > Am I on the right track? Does anybody know the kernel mechanism for > > extracting userspace callchains? Hi Ahmad, a lot of ffmpeg is hand written assembly such as: https://github.com/FFmpeg/FFmpeg/blob/master/libavresample/x86/audio_convert.asm For this to work with dwarf unwinding it needs to have call frame information: https://sourceware.org/binutils/docs/as/CFI-directives.html Thanks, Ian > > Please accept my apology for my frequent questions. I tried to get > > around the problem, myself, but it has taken more than three complete > > days and I'm stuck! > > I really appreciate any suggestions. > > No problem, but please note that perf questions are more likely to be > answered via: linux-perf-users@xxxxxxxxxxxxxxx and not > linux-trace-users. As linux-trace-users are more for ftrace and not > perf. > > -- Steve
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