linux-kernel - Re: [PATCH] perf mem: Fix printing PERF_MEM_LVLNUM_{L2

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Message-ID: <6d409278-988b-4c09-adfb-5e075c9b326e@arm.com>
Date: Wed, 25 Sep 2024 21:16:50 +0100
From: Leo Yan <leo.yan@....com>
To: Thomas Falcon <thomas.falcon@...el.com>, peterz@...radead.org,
 mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf mem: Fix printing PERF_MEM_LVLNUM_{L2_MHB|MSC}

On 9/25/2024 7:36 PM, Thomas Falcon wrote:
> 
> 
> With commit 8ec9497d3ef34 ("tools/include: Sync uapi/linux/perf.h
> with the kernel sources"), 'perf mem report' gives an incorrect memory
> access string.
> ...
> 0.02%   1       3644    L5 hit  [.] 0x0000000000009b0e  mlc     [.] 0x00007fce43f59480
> ...
> 
> This occurs because, if no entry exists in mem_lvlnum, perf_mem__lvl_scnprintf
> will default to 'L%d, lvl', which in this case for PERF_MEM_LVLNUM_L2_MHB is 0x05.
> Add entries for PERF_MEM_LVLNUM_L2_MHB and PERF_MEM_LVLNUM_MSC to mem_lvlnum,
> so that the correct strings are printed.
> ...
> 0.02%   1       3644    L2 MHB hit      [.] 0x0000000000009b0e  mlc     [.] 0x00007fce43f59480
> ...
> 
> Fixes: 8ec9497d3ef34 ("tools/include: Sync uapi/linux/perf.h with the kernel sources")
> Suggested-by: Kan Liang <kan.liang@...ux.intel.com>
> Signed-off-by: Thomas Falcon <thomas.falcon@...el.com>
> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

This change is fine for me. But for later avoid same issues, I would like to
improve a bit:

static const char * const mem_lvlnum[] = {
       [PERF_MEM_LVLNUM_L1] = "L1",
       [PERF_MEM_LVLNUM_L2] = "L2",
       [PERF_MEM_LVLNUM_L3] = "L3",
       [PERF_MEM_LVLNUM_L4] = "L4",
       [PERF_MEM_LVLNUM_L2_MHB] = "L2 MHB",
       [PERF_MEM_LVLNUM_MSC] = "Memory-side Cache",
       ...
};

Then in the function perf_mem__lvl_scnprintf() :

   if (mem_lvlnum[lvl])
       l += scnprintf(out + l, sz - l, mem_lvlnum[lvl]);
   else
       l += scnprintf(out + l, sz - l, "Unknown level %d", lvl);

This can help us easily to catch unexpected memory level.

Thanks,
Leo

> ---
>  tools/perf/util/mem-events.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/mem-events.c b/tools/perf/util/mem-events.c
> index 051feb93ed8d..c630aca5bd93 100644
> --- a/tools/perf/util/mem-events.c
> +++ b/tools/perf/util/mem-events.c
> @@ -366,6 +366,8 @@ static const char * const mem_lvl[] = {
>  };
> 
>  static const char * const mem_lvlnum[] = {
> +       [PERF_MEM_LVLNUM_L2_MHB] = "L2 MHB",
> +       [PERF_MEM_LVLNUM_MSC] = "Memory-side Cache",
>         [PERF_MEM_LVLNUM_UNC] = "Uncached",
>         [PERF_MEM_LVLNUM_CXL] = "CXL",
>         [PERF_MEM_LVLNUM_IO] = "I/O",
> --
> 2.46.0
> 
>