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

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Message-ID: <b27f97d12329452bb95c1345a0bbdd3f@intel.com>
Date:   Sun, 17 Jan 2021 14:44:04 +0000
From:   "Zhang, Rui" <rui.zhang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
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



> -----Original Message-----
> From: Peter Zijlstra <peterz@...radead.org>
> Sent: Saturday, January 16, 2021 8:48 PM
> 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 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.

Well, yes.
Before SPR, this is just a potential issue. But things on SPR suggests that this potential issue may become a real one.
So are you suggesting me to also include the SPR information as the justification of this patch?

Thanks,
rui