linux-kernel - Re: [PATCH RFC 0/7] perf pmu-events: Support event aliasing for system PMUs

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Date:   Tue, 18 Feb 2020 12:57:07 +0000
From:   Will Deacon <will@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, ak@...ux.intel.com,
        linuxarm@...wei.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        james.clark@....com, zhangshaokun@...ilicon.com,
        robin.murphy@....com
Subject: Re: [PATCH RFC 0/7] perf pmu-events: Support event aliasing for
 system PMUs

On Fri, Jan 24, 2020 at 10:34:58PM +0800, John Garry wrote:
> Currently event aliasing for only CPU and uncore PMUs is supported. In
> fact, only uncore PMUs aliasing for when the uncore PMUs are fixed for a
> CPU is supported, which may not always be the case for certain
> architectures.
> 
> This series adds support for PMU event aliasing for system and other
> uncore PMUs which are not fixed to a specific CPU.
> 
> For this, we introduce support for another per-arch mapfile, which maps a
> particular system identifier to a set of system PMU events for that
> system. This is much the same as what we do for CPU event aliasing.
> 
> To support this, we need to change how we match a PMU to a mapfile,
> whether it should use a CPU or system mapfile. For this we do the
> following:
> 
> - For CPU PMU, we always match for the event mapfile based on the CPUID.
>   This has not changed.
> 
> - For an uncore or system PMU, we match first based on the SYSID (if set).
>   If this fails, then we match on the CPUID.
> 
>   This works for x86, as x86 would not have any system mapfiles for uncore
>   PMUs (and match on the CPUID).
> 
> Initial reference support is also added for ARM SMMUv3 PMCG (Performance
> Monitor Event Group) PMU for HiSilicon hip08 platform with only a single
> event so far - see driver in drivers/perf/arm_smmuv3_pmu.c for that driver.

Why don't we just expose SMMU_IIDR in the SMMUv3 PMU directory, so that
you can key off that? I'm nervous about coming up with a global "SYSID"
when we don't have the ability to standardise anything in that space.

Will