linux-kernel - Re: [RFC PATCH V2 4/9] perf/x86: Enable post-processing monotonic raw conversion

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Date:   Tue, 14 Feb 2023 21:55:53 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>, jstultz@...gle.com,
        peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     sboyd@...nel.org, eranian@...gle.com, namhyung@...nel.org,
        ak@...ux.intel.com, adrian.hunter@...el.com,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [RFC PATCH V2 4/9] perf/x86: Enable post-processing monotonic
 raw conversion

On Tue, Feb 14 2023 at 15:21, Kan Liang wrote:
> On 2023-02-14 3:02 p.m., Thomas Gleixner wrote:
>> 
>> What guarantees that the clocksource used by the timekeeping core is
>> actually TSC? Nothing at all. You cannot make assumptions here.
>> 
>
> Yes, you are right.
> I will add a check to make sure the clocksource is TSC when perf does
> the conversion.
>
> Could you please comment on whether the patch is in the right direction?
> This V2 patch series expose the kernel internal conversion information
> into the user space. Is it OK for you?

Making the conversion info an ABI is suboptimal at best. I'm still
trying to wrap my brain around all of this. Will reply over there once
my confusion subsides.

Thanks,

        tglx