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From:   Bryton Lee <brytonlee01@gmail.com>
Date:   Wed, 11 May 2022 09:35:26 +0800
Message-ID: <CAC2pzGdkXz+wJsiSLOV5quMugXDvbMbF-WpiJshXfMM9Qt3FRQ@mail.gmail.com>
Subject: Re: [PATCH v2] perf tools: fix callstack entries and nr print message
To:     jolsa@kernel.org, linux-perf-users@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     ak@linux.intel.com, likexu@tencent.com, chengdongli@tencent.com,
        mark.rutland@arm.com, mingo@redhat.com,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        alexander.shishkin@linux.intel.com, irogers@google.com,
        german.gomez@arm.com, rickyman7@gmail.com,
        Namhyung Kim <namhyung@kernel.org>, peterz@infradead.org,
        alexey.v.bayduraev@linux.intel.com
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Hi Jiri,

Could you kindly review my patch again? I sent out my updates
yesterday. I am happy to know your guidance.

Thanks,
Chengdong

On Tue, May 10, 2022 at 8:41 AM Chengdong Li <brytonlee01@gmail.com> wrote:
>
> From: Chengdong Li <chengdongli@tencent.com>
>
> when generating callstack information from branch_stack(Intel LBR),
> the actual number of callstack entry should be bigger than the number
> of branch_stack, for example:
>
>         branch_stack records:
>                 B() -> C()
>                 A() -> B()
>         converted callstack records should be:
>                 C()
>                 B()
>                 A()
> though, the number of callstack equals
> to the number of branch stack plus 1.
>
> This patch fixes above issue in branch_stack__printf(). For example,
>
>         # echo 'scale=2000; 4*a(1)' > cmd
>         # perf record --call-graph lbr bc -l < cmd
>
> Before applying this patch, `perf script -D` output:
>
>         1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
>         ... LBR call chain: nr:8
>         .....  0: fffffffffffffe00
>         .....  1: 000000000040a410
>         .....  2: 000000000040573c
>         .....  3: 0000000000408650
>         .....  4: 00000000004022f2
>         .....  5: 00000000004015f5
>         .....  6: 00007f5ed6dcb553
>         .....  7: 0000000000401698
>         ... FP chain: nr:2
>         .....  0: fffffffffffffe00
>         .....  1: 000000000040a6d8
>         ... branch callstack: nr:6    # which is not consistent with LBR records.
>         .....  0: 000000000040a410
>         .....  1: 0000000000408650    # ditto
>         .....  2: 00000000004022f2
>         .....  3: 00000000004015f5
>         .....  4: 00007f5ed6dcb553
>         .....  5: 0000000000401698
>          ... thread: bc:17990
>          ...... dso: /usr/bin/bc
>         bc 17990 1220022.677386:     894172 cycles:
>                           40a410 [unknown] (/usr/bin/bc)
>                           40573c [unknown] (/usr/bin/bc)
>                           408650 [unknown] (/usr/bin/bc)
>                           4022f2 [unknown] (/usr/bin/bc)
>                           4015f5 [unknown] (/usr/bin/bc)
>                     7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
>                           401698 [unknown] (/usr/bin/bc)
>
> After applied:
>
>         1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
>         ... LBR call chain: nr:8
>         .....  0: fffffffffffffe00
>         .....  1: 000000000040a410
>         .....  2: 000000000040573c
>         .....  3: 0000000000408650
>         .....  4: 00000000004022f2
>         .....  5: 00000000004015f5
>         .....  6: 00007f5ed6dcb553
>         .....  7: 0000000000401698
>         ... FP chain: nr:2
>         .....  0: fffffffffffffe00
>         .....  1: 000000000040a6d8
>         ... branch callstack: nr:7
>         .....  0: 000000000040a410
>         .....  1: 000000000040573c
>         .....  2: 0000000000408650
>         .....  3: 00000000004022f2
>         .....  4: 00000000004015f5
>         .....  5: 00007f5ed6dcb553
>         .....  6: 0000000000401698
>          ... thread: bc:17990
>          ...... dso: /usr/bin/bc
>         bc 17990 1220022.677386:     894172 cycles:
>                           40a410 [unknown] (/usr/bin/bc)
>                           40573c [unknown] (/usr/bin/bc)
>                           408650 [unknown] (/usr/bin/bc)
>                           4022f2 [unknown] (/usr/bin/bc)
>                           4015f5 [unknown] (/usr/bin/bc)
>                     7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
>                           401698 [unknown] (/usr/bin/bc)
>
> Change from v1:
>         - refined code style according to Jiri's review comments.
>
> Signed-off-by: Chengdong Li <chengdongli@tencent.com>
> ---
>  tools/perf/util/session.c | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f9a320694b85..a7f93f5a1ac8 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1151,9 +1151,20 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>         struct branch_entry *entries = perf_sample__branch_entries(sample);
>         uint64_t i;
>
> -       printf("%s: nr:%" PRIu64 "\n",
> -               !callstack ? "... branch stack" : "... branch callstack",
> -               sample->branch_stack->nr);
> +       if (!callstack) {
> +               printf("%s: nr:%" PRIu64 "\n", "... branch stack", sample->branch_stack->nr);
> +       } else {
> +               /* the reason of adding 1 to nr is because after expanding
> +                * branch stack it generates nr + 1 callstack records. e.g.,
> +                *         B()->C()
> +                *         A()->B()
> +                * the final callstack should be:
> +                *         C()
> +                *         B()
> +                *         A()
> +                */
> +               printf("%s: nr:%" PRIu64 "\n", "... branch callstack", sample->branch_stack->nr+1);
> +       }
>
>         for (i = 0; i < sample->branch_stack->nr; i++) {
>                 struct branch_entry *e = &entries[i];
> @@ -1169,8 +1180,13 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>                                 (unsigned)e->flags.reserved,
>                                 e->flags.type ? branch_type_name(e->flags.type) : "");
>                 } else {
> -                       printf("..... %2"PRIu64": %016" PRIx64 "\n",
> -                               i, i > 0 ? e->from : e->to);
> +                       if (i == 0) {
> +                               printf("..... %2"PRIu64": %016" PRIx64 "\n"
> +                                      "..... %2"PRIu64": %016" PRIx64 "\n",
> +                                               i, e->to, i+1, e->from);
> +                       } else {
> +                               printf("..... %2"PRIu64": %016" PRIx64 "\n", i+1, e->from);
> +                       }
>                 }
>         }
>  }
> --
> 2.27.0
>


-- 
Best Regards

Bryton.Lee