Linux-Trace-Users Archive on lore.kernel.org
 help / color / Atom feed
From: ahmadkhorrami <ahmadkhorrami@ut.ac.ir>
To: Linux-trace Users <linux-trace-users@vger.kernel.org>
Subject: Perf Script Erroneous User Stack Trace
Date: Sun, 14 Jun 2020 18:13:21 +0430
Message-ID: <816cb5f558cd0e528812dff2168ef4ca@ut.ac.ir> (raw)

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?

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.

Regards.

             reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-14 13:43 ahmadkhorrami [this message]
2020-06-15 20:31 ` Steven Rostedt
2020-06-15 20:53   ` Ian Rogers
2020-06-16 10:38     ` Sp! " ahmadkhorrami
2020-06-16 14:37       ` ahmadkhorrami
2020-06-16 16:20         ` Milian Wolff
2020-06-16 17:06           ` ahmadkhorrami
2020-06-16 17:42           ` ahmadkhorrami
2020-06-16 10:26   ` ahmadkhorrami

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=816cb5f558cd0e528812dff2168ef4ca@ut.ac.ir \
    --to=ahmadkhorrami@ut.ac.ir \
    --cc=linux-trace-users@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Trace-Users Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-trace-users/0 linux-trace-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-trace-users linux-trace-users/ https://lore.kernel.org/linux-trace-users \
		linux-trace-users@vger.kernel.org
	public-inbox-index linux-trace-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-trace-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git