Hi Arnaldo,
Could you please review the patch?
I've already updated the patch description to try to address your concern.
Please let me know if you have any questions.
Thanks,
Kan
>
> From: Kan Liang <kan.li...@intel.com>
>
> Currently, the perf diff only works with same binaries. That's because it
> compares the symbol start address. It doesn't work if the perf.data comes
> from different binaries. This patch matches the symbol names.
>
> Actually, perf diff once intended to compare the symbol names.
> The commit as below can look for a pair by name.
> 604c5c92972d (perf diff: Change the default sort order to "dso,symbol")
> However, at that time, perf diff used a global list of dsos. That means the
> binaries which has same name can only be loaded once. That's a problem
> for different binaries compare. For example, we have an old binary and an
> updated binary. They very likely have same name and most of the function,
> so only dsos from old binary will be loaded. When processing the data from
> updated binary, perf still use the symbol information from old binary.
> That's wrong.
>
> Then the commit as below used IP to replace symbol name.
> 9c443dfdd31e ("perf diff: Fix support for all --sort combinations") From that
> time, perf diff starts to compare the symbol address.
>
> The global dsos is discarded from a patch in 2010.
> a1645ce12adb ("perf: 'perf kvm' tool for monitoring guest performance
> from host") However, at that time, perf diff already compared by address.
> So perf diff cannot work for different binaries as well.
>
> This patch actually rolls back the perf diff to original design. The document
> is also changed, so everybody knows the original design is to compare the
> symbol names.
>
> Here is an examples.
> The only difference between example_v1.c and example_v2.c is the
> location of f2 and f3. There is no change in behavior, but the previous perf
> diff display the wrong differential profile.
>
> example_v1.c
> noinline void f3(void)
> {
> volatile int i;
> for (i = 0; i < 10000;) {
>
> if(i%2)
> i++;
> else
> i++;
> }
> }
>
> noinline void f2(void)
> {
> volatile int a = 100, b, c;
> for (b = 0; b < 10000; b++)
> c = a * b;
>
> }
>
> noinline void f1(void)
> {
> f2();
> f3();
> }
>
> int main()
> {
> int i;
> for (i = 0; i < 100000; i++)
> f1();
> }
>
> example_v2.c
> noinline void f2(void)
> {
> volatile int a = 100, b, c;
> for (b = 0; b < 10000; b++)
> c = a * b;
> }
>
> noinline void f3(void)
> {
> volatile int i;
> for (i = 0; i < 10000;) {
> if(i%2)
> i++;
> else
> i++;
> }
> }
>
> noinline void f1(void)
> {
> f2();
> f3();
> }
>
> int main()
> {
> int i;
> for (i = 0; i < 100000; i++)
> f1();
> }
>
> [lk@localhost perf_diff]$ gcc example_v1.c -o example [lk@localhost
> perf_diff]$ perf record -o example_v1.data ./example [ perf record:
> Woken up 4 times to write data ] [ perf record: Captured and wrote 0.813
> MB example_v1.data (~35522
> samples) ]
>
> [lk@localhost perf_diff]$ gcc example_v2.c -o example [lk@localhost
> perf_diff]$ perf record -o example_v2.data ./example [ perf record:
> Woken up 4 times to write data ] [ perf record: Captured and wrote 0.824
> MB example_v2.data (~36015
> samples) ]
>
> Old perf diff result.
> [lk@localhost perf_diff]$ perf diff example_v1.data example_v2.data
> Event 'cycles'
> Baseline Delta Shared Object Symbol
> ........ ....... ................ ...............................
>
> [kernel.vmlinux] [k] __perf_event_task_sched_out
> 0.00% [kernel.vmlinux] [k] apic_timer_interrupt
> [kernel.vmlinux] [k] idle_cpu
> [kernel.vmlinux] [k] intel_pstate_timer_func
> [kernel.vmlinux] [k] native_read_msr_safe
> 0.00% [kernel.vmlinux] [k] native_read_tsc
> 0.00% [kernel.vmlinux] [k] native_write_msr_safe
> [kernel.vmlinux] [k] ntp_tick_length
> 0.00% [kernel.vmlinux] [k] rb_erase
> 0.00% [kernel.vmlinux] [k] tick_sched_timer
> 0.00% [kernel.vmlinux] [k] unmap_single_vma
> 0.00% [kernel.vmlinux] [k] update_wall_time
> 0.00% example [.] f1
> 46.24% example [.] f2
> 53.71% -7.55% example [.] f3
> +53.81% example [.] f3
> 0.02% example [.] main
>
> New perf diff result.
> [lk@localhost perf_diff]$ perf diff example_v1.data example_v2.data
> [kernel.vmlinux] [k] __perf_event_task_sched_out
> 0.00% [kernel.vmlinux] [k] apic_timer_interrupt
> [kernel.vmlinux] [k] idle_cpu
> [kernel.vmlinux] [k] intel_pstate_timer_func
> [kernel.vmlinux] [k] native_read_msr_safe
> 0.00% [kernel.vmlinux] [k] native_read_tsc
> 0.00% [kernel.vmlinux] [k] native_write_msr_safe
> [kernel.vmlinux] [k] ntp_tick_length
> 0.00% [kernel.vmlinux] [k] rb_erase
> 0.00% [kernel.vmlinux] [k] tick_sched_timer
> 0.00% [kernel.vmlinux] [k] unmap_single_vma
> 0.00% [kernel.vmlinux] [k] update_wall_time
> 0.00% example [.] f1
> 46.24% -0.08% example [.] f2
> 53.71% +0.11% example [.] f3
> 0.02% example [.] main
>
> Signed-off-by: Kan Liang <kan.li...@intel.com>
> Acked-by: Namhyung Kim <namhy...@kernel.org>
> Acked-by: Jiri Olsa <jo...@kernel.org>
>
> ---
>
> Changes since V4:
> - Seperate from old patch set
> - Add an example in changelog
> - Update man page
>
> Changes since V5:
> - Correct patch style
>
> Changes since V6:
> - Update description
>
> tools/perf/Documentation/perf-diff.txt | 5 +++++
> tools/perf/util/sort.c | 9 +++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/tools/perf/Documentation/perf-diff.txt
> b/tools/perf/Documentation/perf-diff.txt
> index e463caa..5182661 100644
> --- a/tools/perf/Documentation/perf-diff.txt
> +++ b/tools/perf/Documentation/perf-diff.txt
> @@ -20,6 +20,11 @@ If no parameters are passed it will assume
> perf.data.old and perf.data.
> The differential profile is displayed only for events matching both
> specified perf.data files.
>
> +If no parameters are passed the samples will be sorted by dso and symbol.
> +As the perf.data files could come from different binaries, the symbols
> +addresses could vary. So perf diff is based on the comparison of the
> +files and symbols name.
> +
> OPTIONS
> -------
> -D::
> diff --git a/tools/perf/util/sort.c b/tools/perf/util/sort.c index
> 7a39c1e..4593f36 100644
> --- a/tools/perf/util/sort.c
> +++ b/tools/perf/util/sort.c
> @@ -1463,6 +1463,15 @@ int sort_dimension__add(const char *tok)
> sort__has_parent = 1;
> } else if (sd->entry == &sort_sym) {
> sort__has_sym = 1;
> + /*
> + * perf diff displays the performance difference
> amongst
> + * two or more perf.data files. Those files could
> come
> + * from different binaries. So we should not
> compare
> + * their ips, but the name of symbol.
> + */
> + if (sort__mode == SORT_MODE__DIFF)
> + sd->entry->se_collapse = sort__sym_sort;
> +
> } else if (sd->entry == &sort_dso) {
> sort__has_dso = 1;
> }
> --
> 1.7.11.7
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