Re: [PATCH v2] perf: libdw support for powerpc [ping]

Hi Mark,

On Tuesday 13 June 2017 05:14 PM, Mark Wielaard wrote:

I see the same on very short runs. But when doing a slightly longer run,
even just using ls -lahR, which does some more work, then I do see user
backtraces. They are still missing for some of the early samples though.
It is as if there is a stack/memory address mismatch when the probe is
"too early" in ld.so.

Could you do a test run on some program that does some more work to see
if you never get any user stack traces, or if you only not get them for
some specific probes?

Thanks for checking. I tried a proper workload this time, but I still
don't see any userspace callchain getting unwound.

  $ ./perf record --call-graph=dwarf -- zip -q -r temp.zip .
  [ perf record: Woken up 2891 times to write data ]
  [ perf record: Captured and wrote 723.290 MB perf.data (87934 samples) ]


With libdw:

 $ LD_LIBRARY_PATH=/home/ravi/elfutils-git/usr/local/lib:\
    /home/ravi/elfutils-git/usr/local/lib/elfutils/:$LD_LIBRARY_PATH\
    ./perf script

  zip 16699  6857.354633:      37371 cycles:u:
                   ecedc xmon_core (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   8c4fc __hash_page_64K (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   83450 hash_preload (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   7cc34 update_mmu_cache (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                  330064 alloc_set_pte (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                  330efc do_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                  334580 __handle_mm_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                  335040 handle_mm_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   7bf94 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   7bec4 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   7be78 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                   1a4f8 handle_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)

  zip 16699  6857.354663:     300677 cycles:u:

  zip 16699  6857.354895:     584131 cycles:u:

  zip 16699  6857.355312:     589687 cycles:u:

  zip 16699  6857.355606:     560142 cycles:u:


With libunwind:

$ ./perf script

  zip 16699  6857.354633:      37371 cycles:u:
                     ecedc xmon_core (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     8c4fc __hash_page_64K (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     83450 hash_preload (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     7cc34 update_mmu_cache (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                    330064 alloc_set_pte (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                    330efc do_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                    334580 __handle_mm_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                    335040 handle_mm_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     7bf94 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     7bec4 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     7be78 do_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                     1a4f8 handle_page_fault (/usr/lib/debug/lib/modules/4.11.0-3.el7.ppc64le/vmlinux)
                      1920 _start (/usr/lib64/ld-2.17.so)

  zip 16699  6857.354663:     300677 cycles:u:
                      fa38 _dl_new_object (/usr/lib64/ld-2.17.so)
                      3073 dl_main (/usr/lib64/ld-2.17.so)
                     2045b _dl_sysdep_start (/usr/lib64/ld-2.17.so)
                      1c7f _dl_start_final (/usr/lib64/ld-2.17.so)
                      5ce7 _dl_start (/usr/lib64/ld-2.17.so)
                      1937 _start (/usr/lib64/ld-2.17.so)

  zip 16699  6857.354895:     584131 cycles:u:
                     103d0 _dl_relocate_object (/usr/lib64/ld-2.17.so)

  zip 16699  6857.355312:     589687 cycles:u:
                      df68 do_lookup_x (/usr/lib64/ld-2.17.so)
                      e8d7 _dl_lookup_symbol_x (/usr/lib64/ld-2.17.so)
                     14bb3 _dl_fixup (/usr/lib64/ld-2.17.so)
                     1ef37 _dl_runtime_resolve (/usr/lib64/ld-2.17.so)
                     20bf7 copy_args (/usr/bin/zip)
                      286f main (/usr/bin/zip)
                     2497f generic_start_main.isra.0 (/usr/lib64/libc-2.17.so)
                     24b73 __libc_start_main (/usr/lib64/libc-2.17.so)

  zip 16699  6857.355606:     560142 cycles:u:
                     84764 _IO_getc (/usr/lib64/libc-2.17.so)
                      c4d7 find_next_signature (/usr/bin/zip)
                     15c8b readzipfile (/usr/bin/zip)
                      3477 main (/usr/bin/zip)
                     2497f generic_start_main.isra.0 (/usr/lib64/libc-2.17.so)
                     24b73 __libc_start_main (/usr/lib64/libc-2.17.so)


Right now, I'm busy with few other things so I'm not able to dig further.
But I can look into this next week or so.

Thanks,
Ravi