linux-kernel - Re: [PATCH] perf/x86/amd: Make HW_CACHE_REFERENCES and HW_CACHE

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Date:	Thu, 11 Aug 2016 18:41:50 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] perf/x86/amd: Make HW_CACHE_REFERENCES and
 HW_CACHE_MISSES measure L2

Drop stable from CC.

On Thu, Aug 11, 2016 at 04:21:42PM +0100, Matt Fleming wrote:
> While the Intel PMU monitors the LLC when perf enables the
> HW_CACHE_REFERENCES and HW_CACHE_MISSES events, these events monitor
> L1 instruction cache fetches (0x0080) and instruction cache misses
> (0x0081) on the AMD PMU.
> 
> This is extremely confusing when monitoring the same workload across
> Intel and AMD machines, since parameters like,
> 
>   $ perf stat -e cache-references,cache-misses
> 
> measure completely different things.
> 
> Instead, make the AMD PMU measure instruction/data cache fill requests
> to the L2 and instruction/data cache misses in the L2 when
> HW_CACHE_REFERENCES and HW_CACHE_MISSES are enabled, respectively.
> That way the events measure unified caches on both platforms.

I guess that's closer.

Even though LLC is not always L2 on AMD (some have L3). Btw,
what are the exact events for PERF_COUNT_HW_CACHE_REFERENCES and
PERF_COUNT_HW_CACHE_MISSES called on Intel?

I could try to find better/more fitting event selectors on AMD...

> Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: <stable@...r.kernel.org>
> ---
>  arch/x86/events/amd/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index e07a22bb9308..8fd8bf79f32b 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -119,8 +119,8 @@ static const u64 amd_perfmon_event_map[PERF_COUNT_HW_MAX] =
>  {
>    [PERF_COUNT_HW_CPU_CYCLES]			= 0x0076,
>    [PERF_COUNT_HW_INSTRUCTIONS]			= 0x00c0,
> -  [PERF_COUNT_HW_CACHE_REFERENCES]		= 0x0080,
> -  [PERF_COUNT_HW_CACHE_MISSES]			= 0x0081,
> +  [PERF_COUNT_HW_CACHE_REFERENCES]		= 0x037d,
> +  [PERF_COUNT_HW_CACHE_MISSES]			= 0x037e,
>    [PERF_COUNT_HW_BRANCH_INSTRUCTIONS]		= 0x00c2,
>    [PERF_COUNT_HW_BRANCH_MISSES]			= 0x00c3,
>    [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND]	= 0x00d0, /* "Decoder empty" event */

Btw, there's also amd_event_mapping in arch/x86/kvm/pmu_amd.c which has
duplicated amd_perfmon_event_map. Would need adjusting too.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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