linux-kernel - Re: [PATCH 2/3] perf/x86/rapl: Fix energy counter detection

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Message-ID: <YALgm2b0YNkO7Qtd@hirez.programming.kicks-ass.net>
Date:   Sat, 16 Jan 2021 13:48:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Zhang, Rui" <rui.zhang@...el.com>
Cc:     "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH 2/3] perf/x86/rapl: Fix energy counter detection

On Sat, Jan 16, 2021 at 08:19:35AM +0000, Zhang, Rui wrote:
> 
> 
> > -----Original Message-----
> > From: Peter Zijlstra <peterz@...radead.org>
> > Sent: Saturday, January 16, 2021 4:03 AM
> > To: Zhang, Rui <rui.zhang@...el.com>
> > Cc: mingo@...hat.com; acme@...nel.org; mark.rutland@....com;
> > alexander.shishkin@...ux.intel.com; jolsa@...hat.com;
> > namhyung@...nel.org; linux-kernel@...r.kernel.org; x86@...nel.org;
> > kan.liang@...ux.intel.com; ak@...ux.intel.com
> > Subject: Re: [PATCH 2/3] perf/x86/rapl: Fix energy counter detection
> > Importance: High
> > 
> > On Fri, Jan 15, 2021 at 05:22:07PM +0800, Zhang Rui wrote:
> > > In the RAPL ENERGY_COUNTER MSR, only the lower 32bits represent the
> > > energy counter, and the higher 32bits are reserved.
> > >
> > > Add the MSR mask for these MSRs to fix a problem that the RAPL PMU
> > > events are added erroneously when higher 32bits contain non-zero value.
> > 
> > Why would these high bits be non-zero?
> 
> On SPR platform, the high bits of Psys energy counter are reused for other purpose.
> High bits for other RAPL domains energy counters still return 0.
> 
> I didn't mention this because I thought this patch should be okay as a generic fix.

But it doesn't fix anything.. there's not anything broken, except on
that daft SPR thing.