linux-kernel - Re: [PATCH 2/2] arm64: pmu: Wire-up L2 cache events for ARMv8 PMUv3

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Date:   Tue, 25 Apr 2017 13:44:28 +0100
From:   Will Deacon <will.deacon@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, alcooperx@...il.com,
        opendmb@...il.com, Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] arm64: pmu: Wire-up L2 cache events for ARMv8 PMUv3

Hi Florian,

On Thu, Apr 20, 2017 at 12:05:46PM -0700, Florian Fainelli wrote:
> The ARMv8 PMUv3 cache map did not include the L2 cache events, add
> them.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  arch/arm64/kernel/perf_event.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index 4f011cdd756d..a664c575f3fd 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -264,6 +264,11 @@ static const unsigned armv8_pmuv3_perf_cache_map[PERF_COUNT_HW_CACHE_MAX]
>  	[C(L1I)][C(OP_READ)][C(RESULT_ACCESS)]	= ARMV8_PMUV3_PERFCTR_L1I_CACHE,
>  	[C(L1I)][C(OP_READ)][C(RESULT_MISS)]	= ARMV8_PMUV3_PERFCTR_L1I_CACHE_REFILL,
>  
> +	[C(LL)][C(OP_READ)][C(RESULT_ACCESS)]	= ARMV8_PMUV3_PERFCTR_L2D_CACHE,
> +	[C(LL)][C(OP_READ)][C(RESULT_MISS)]	= ARMV8_PMUV3_PERFCTR_L2D_CACHE_REFILL,
> +	[C(LL)][C(OP_WRITE)][C(RESULT_ACCESS)]	= ARMV8_PMUV3_PERFCTR_L2D_CACHE,
> +	[C(LL)][C(OP_WRITE)][C(RESULT_MISS)]	= ARMV8_PMUV3_PERFCTR_L2D_CACHE_REFILL,

I don't think this is correct in general. 'LL' stands for "last-level",
which may be L3 or even a system cache in the interconnect. Tying that to L2
is the wrong thing to do from perf's generic event perspective.

I'm ok with what you're proposing for A53 (where the PMU can only count
events out to the L2), but I'm reluctant to make this change for the generic
PMUv3 events.

Will