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

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Date:   Thu, 27 Apr 2017 18:36:42 +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

On Tue, Apr 25, 2017 at 10:13:51AM -0700, Florian Fainelli wrote:
> On 04/25/2017 05:44 AM, Will Deacon wrote:
> > 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.
> 
> That makes sense, shall I resubmit the first patch by itself or can you
> or Catalin take it as-is?

I'll talk to Catalin tomorrow and try to get the A53 bit queued.

Will