linux-kernel - Re: [PATCH v3] x86/cpu/amd: Enable the fixed Instructions Retired counter IRPERF

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Date:   Tue, 18 Feb 2020 22:54:11 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Babu Moger <babu.moger@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Frank van der Linden <fllinden@...zon.com>,
        "H . Peter Anvin" <hpa@...or.com>, Huang Rui <ray.huang@....com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Jan Beulich <jbeulich@...e.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Luwei Kang <luwei.kang@...el.com>,
        Martin Liška <mliska@...e.cz>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3] x86/cpu/amd: Enable the fixed Instructions Retired
 counter IRPERF

On Tue, Feb 18, 2020 at 03:35:25PM -0600, Kim Phillips wrote:
> The only reason to have it show in /proc/cpuinfo is for userspace,
> but they can check for a nonzero count prior to using, instead.

How is userspace going to check it? perf tool or people *can* check it?
If perf is going to check it then I'm fine with having the bug bit in
/proc/cpuinfo along with a patch for perf adding usage for it.

If not and people in userspace can maybe check it but they probably
won't then adding that bug bit would be a waste of bit.

> Let me know if you'd like me to send a v4, or if you will just apply
> this version of yours.

I can take the simpler version for now. If you still want to have perf
tool check the bit, you could submit a new patch adding that bug bit
along with a perf tool patch using it...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette