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[PATCH] perf report: include partial stacks unwound with libdw

Started byMilian Wolff <milian.wolff@kdab.com>
First post2017-06-01 23:10 +0200
Last post2017-06-07 18:10 +0200
Articles 3 — 3 participants

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  [PATCH] perf report: include partial stacks unwound with libdw Milian Wolff <milian.wolff@kdab.com> - 2017-06-01 23:10 +0200
    Re: [PATCH] perf report: include partial stacks unwound with libdw Arnaldo Carvalho de Melo <acme@redhat.com> - 2017-06-02 17:00 +0200
    [tip:perf/urgent] perf report: Include partial stacks unwound with  libdw tip-bot for Milian Wolff <tipbot@zytor.com> - 2017-06-07 18:10 +0200

#1655765 — [PATCH] perf report: include partial stacks unwound with libdw

FromMilian Wolff <milian.wolff@kdab.com>
Date2017-06-01 23:10 +0200
Subject[PATCH] perf report: include partial stacks unwound with libdw
Message-ID<tNFvY-81a-11@gated-at.bofh.it>
So far the whole stack was thrown away when any error occurred
before the maximum stack depth was unwound. This is actually a very
common scenario though. The stacks that got unwound so far are
still interesting. This removes a large chunk of differences when
comparing perf script output for libunwind and libdw perf unwinding.

E.g. with libunwind:

~~~~~
heaptrack_gui  2228 135073.388524:     479408 cycles:
        ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
        ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
        ffffffff811cf5ed mmap_region ([kernel.kallsyms])
        ffffffff811cfe6b do_mmap ([kernel.kallsyms])
        ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
        ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
        ffffffff81033acb sys_mmap ([kernel.kallsyms])
        ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])
                   192ca mmap64 (/usr/lib/ld-2.25.so)
                    59a9 _dl_map_object_from_fd (/usr/lib/ld-2.25.so)
                    83d0 _dl_map_object (/usr/lib/ld-2.25.so)
                    cda1 openaux (/usr/lib/ld-2.25.so)
                   1834f _dl_catch_error (/usr/lib/ld-2.25.so)
                    cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
                    3481 dl_main (/usr/lib/ld-2.25.so)
                   17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
                    4d37 _dl_start (/usr/lib/ld-2.25.so)
                     d87 _start (/usr/lib/ld-2.25.so)

heaptrack_gui  2228 135073.388677:     611329 cycles:
                   1a3e0 strcmp (/usr/lib/ld-2.25.so)
                    82b2 _dl_map_object (/usr/lib/ld-2.25.so)
                    cda1 openaux (/usr/lib/ld-2.25.so)
                   1834f _dl_catch_error (/usr/lib/ld-2.25.so)
                    cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
                    3481 dl_main (/usr/lib/ld-2.25.so)
                   17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
                    4d37 _dl_start (/usr/lib/ld-2.25.so)
                     d87 _start (/usr/lib/ld-2.25.so)
~~~~~

With libdw without this patch:

~~~~~
heaptrack_gui  2228 135073.388524:     479408 cycles:
        ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
        ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
        ffffffff811cf5ed mmap_region ([kernel.kallsyms])
        ffffffff811cfe6b do_mmap ([kernel.kallsyms])
        ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
        ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
        ffffffff81033acb sys_mmap ([kernel.kallsyms])
        ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])

heaptrack_gui  2228 135073.388677:     611329 cycles:
~~~~~

With this patch applied, the libdw unwinder will produce the same
output as the libunwind unwinder.

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
---
 tools/perf/util/unwind-libdw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index 943a06291587..b4c20124d2ee 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -224,7 +224,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
 
 	err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);
 
-	if (err && !ui->max_stack)
+	if (err && ui->max_stack != max_stack)
 		err = 0;
 
 	/*
-- 
2.13.0

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#1656314

FromArnaldo Carvalho de Melo <acme@redhat.com>
Date2017-06-02 17:00 +0200
Message-ID<tNWds-2wl-25@gated-at.bofh.it>
In reply to#1655765
Em Thu, Jun 01, 2017 at 11:00:21PM +0200, Milian Wolff escreveu:
> With this patch applied, the libdw unwinder will produce the same
> output as the libunwind unwinder.

> +++ b/tools/perf/util/unwind-libdw.c
> @@ -224,7 +224,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
>  
>  	err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);
>  
> -	if (err && !ui->max_stack)
> +	if (err && ui->max_stack != max_stack)
>  		err = 0;

Simple enough, thanks a lot, applied!

- Arnaldo

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#1659954 — [tip:perf/urgent] perf report: Include partial stacks unwound with libdw

Fromtip-bot for Milian Wolff <tipbot@zytor.com>
Date2017-06-07 18:10 +0200
Subject[tip:perf/urgent] perf report: Include partial stacks unwound with libdw
Message-ID<tPLGV-rD-1@gated-at.bofh.it>
In reply to#1655765
Commit-ID:  5ea0416f51cc93436bbe497c62ab49fd9cb245b6
Gitweb:     http://git.kernel.org/tip/5ea0416f51cc93436bbe497c62ab49fd9cb245b6
Author:     Milian Wolff <milian.wolff@kdab.com>
AuthorDate: Thu, 1 Jun 2017 23:00:21 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 5 Jun 2017 14:18:03 -0300

perf report: Include partial stacks unwound with libdw

So far the whole stack was thrown away when any error occurred before
the maximum stack depth was unwound. This is actually a very common
scenario though. The stacks that got unwound so far are still
interesting. This removes a large chunk of differences when comparing
perf script output for libunwind and libdw perf unwinding.

E.g. with libunwind:

~~~~~
heaptrack_gui  2228 135073.388524:     479408 cycles:
        ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
        ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
        ffffffff811cf5ed mmap_region ([kernel.kallsyms])
        ffffffff811cfe6b do_mmap ([kernel.kallsyms])
        ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
        ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
        ffffffff81033acb sys_mmap ([kernel.kallsyms])
        ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])
                   192ca mmap64 (/usr/lib/ld-2.25.so)
                    59a9 _dl_map_object_from_fd (/usr/lib/ld-2.25.so)
                    83d0 _dl_map_object (/usr/lib/ld-2.25.so)
                    cda1 openaux (/usr/lib/ld-2.25.so)
                   1834f _dl_catch_error (/usr/lib/ld-2.25.so)
                    cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
                    3481 dl_main (/usr/lib/ld-2.25.so)
                   17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
                    4d37 _dl_start (/usr/lib/ld-2.25.so)
                     d87 _start (/usr/lib/ld-2.25.so)

heaptrack_gui  2228 135073.388677:     611329 cycles:
                   1a3e0 strcmp (/usr/lib/ld-2.25.so)
                    82b2 _dl_map_object (/usr/lib/ld-2.25.so)
                    cda1 openaux (/usr/lib/ld-2.25.so)
                   1834f _dl_catch_error (/usr/lib/ld-2.25.so)
                    cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
                    3481 dl_main (/usr/lib/ld-2.25.so)
                   17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
                    4d37 _dl_start (/usr/lib/ld-2.25.so)
                     d87 _start (/usr/lib/ld-2.25.so)
~~~~~

With libdw without this patch:

~~~~~
heaptrack_gui  2228 135073.388524:     479408 cycles:
        ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
        ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
        ffffffff811cf5ed mmap_region ([kernel.kallsyms])
        ffffffff811cfe6b do_mmap ([kernel.kallsyms])
        ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
        ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
        ffffffff81033acb sys_mmap ([kernel.kallsyms])
        ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])

heaptrack_gui  2228 135073.388677:     611329 cycles:
~~~~~

With this patch applied, the libdw unwinder will produce the same
output as the libunwind unwinder.

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20170601210021.20046-1-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/unwind-libdw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index 943a0629..b4c2012 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -224,7 +224,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
 
 	err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);
 
-	if (err && !ui->max_stack)
+	if (err && ui->max_stack != max_stack)
 		err = 0;
 
 	/*

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