linux-kernel - Re: [PATCH] arm_pmu: Delete incorrect cache event mapping for some armv8

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Message-ID: <CAKTKpr4a12FHkMtFNueWqQbAhT4TLw_4DLDrOD6Tjsbno28U3A@mail.gmail.com>
Date:   Fri, 5 Oct 2018 01:09:33 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Ganapatrao Kulkarni <Ganapatrao.Kulkarni@...ium.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "Nair, Jayachandran" <Jayachandran.Nair@...ium.com>,
        Robert Richter <Robert.Richter@...ium.com>,
        Vadim.Lomovtsev@...ium.com, Jan.Glauber@...ium.com
Subject: Re: [PATCH] arm_pmu: Delete incorrect cache event mapping for some
 armv8_pmuv3 events.

Hi Will,

On Thu, Oct 4, 2018 at 5:51 PM Will Deacon <will.deacon@....com> wrote:
>
> Hi Ganapat,
>
> On Thu, Oct 04, 2018 at 11:12:09AM +0530, Ganapatrao Kulkarni wrote:
> > can you please pull this patch?
>
> I still don't like the idea of just removing events like this, especially
> when other architectures (including some x86 and Power CPUs afaict) playa
> similar games for generic events, and these events do actually appear in
> user code.
>
> I also don't understand why you remove the TLB events. I think that logic
> would imply we should remove all of the events, because we can't distinguish
> prefetches from reads either. If we want to be consistent, then I think
> we should just remove the OP_WRITE events for L1D and BPU -- would you be
> ok with that instead?

IIUC, dTLB-load-misses is mapped to
ARMV8_PMUV3_PERFCTR_L1D_TLB_REFILL(event 0x05) and dTLB-loads is
mapped to ARMV8_PMUV3_PERFCTR_L1D_TLB(0x25). Which are as per spec,
counts TLB access/misses for both memory-read operation and
memory-write operation.

IMO, It won't help in keeping these events, knowingly that their
mapping is not accurate, only thing i can say to users is , dont use
events that are marked as "Hardware cache event"

>
> Also, looking at the code, I think our PMCEID parsing is broken for 8.1
> parts, where the upper 32 bits of the register are offset by 0x4000 in the
> event numbering space.

yes, i did not find any mapping in PMCEIDx registers for
implementation defined events, otherwise we would have remapped at
runtime.

>
> Will

thanks
Ganapat