linux-kernel - Re: [PATCH 0/8] perf/x86: Rework msr probe interface

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Message-ID: <20190528102220.GA4917@krava>
Date:   Tue, 28 May 2019 12:22:20 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 0/8] perf/x86: Rework msr probe interface

On Tue, May 28, 2019 at 12:01:47PM +0200, Peter Zijlstra wrote:
> On Mon, May 27, 2019 at 11:51:21PM +0200, Jiri Olsa wrote:
> > hi,
> > following up on [1], [2] and [3], this patchset adds update
> > attribute groups to pmu, factors out the MSR probe code and
> > use it in msr,cstate* and rapl PMUs.
> > 
> > The functionality stays the same with one exception:
> > the event is not exported if the rdmsr return zero
> > on event's msr.
> 
> That seems a wee bit dangerous, are we sure none of these counters are 0
> by 'accident' when we probe them? I'm thinking esp. things like the Cn
> residency stuff could be 0 simply because we've not been into that state
> yet.

ah right, I can disable that check for cstate pmu
and perhaps for msr pmu as well

It's aiming for rapl counters which could return 0
for unsupported counters, agreed by Kan before:

https://lore.kernel.org/lkml/5fcaf3ae-00d3-f635-74bd-8b81a089133f@linux.intel.com/

jirka

> 
> Other than that, this looks good. Kan?