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Date:   Mon, 1 Oct 2018 15:29:15 +0100
From:   Will Deacon <will.deacon@arm.com>
To:     "Kulkarni, Ganapatrao" <Ganapatrao.Kulkarni@cavium.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "acme@kernel.org" <acme@kernel.org>,
        "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>,
        "Richter, Robert" <Robert.Richter@cavium.com>,
        "Lomovtsev, Vadim" <Vadim.Lomovtsev@cavium.com>,
        Jan Glauber <Jan.Glauber@cavium.com>,
        "gklkml16@gmail.com" <gklkml16@gmail.com>
Subject: Re: [PATCH] arm_pmu: Delete incorrect cache event mapping for some
 armv8_pmuv3 events.
Message-ID: <20181001142914.GD9716@arm.com>
References: <20181001100707.16840-1-ganapatrao.kulkarni@cavium.com>
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Hi Ganapat,

On Mon, Oct 01, 2018 at 10:07:43AM +0000, Kulkarni, Ganapatrao wrote:
> Perf events L1-dcache-load-misses, L1-dcache-store-misses are mapped to
> armv8_pmuv3 (both DT and ACPI) event L1D_CACHE_REFILL. This is incorrect,
> since L1D_CACHE_REFILL counts both load and store misses.
> Similarly the events L1-dcache-loads, L1-dcache-stores, dTLB-load-misses
> and dTLB-loads are wrongly mapped. Hence Deleting all these cache events
> from armv8_pmuv3 cache mapping.
> 
> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
> ---
>  arch/arm64/kernel/perf_event.c | 8 --------
>  1 file changed, 8 deletions(-)

The "generic" events are really implemented on a best-effort basis, as
they rarely tend to map exactly to what the hardware supports. I think
they originally stemmed from the x86 CPU PMU, but that doesn't really
help us.

I had a discussion with Ingo back when we originally implemented perf
because I actually preferred not to implement the generic events at all.
However, he was strongly of the opinion that a best-effort approach was
sufficient to get casual users going with the tool, so that's what we went
with.

Will