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

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Message-ID: <875yc4rp68.ffs@tglx>
Date:   Tue, 14 Feb 2023 21:02:23 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     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,
        Kan Liang <kan.liang@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [RFC PATCH V2 4/9] perf/x86: Enable post-processing monotonic
 raw conversion

Kan!

On Mon, Feb 13 2023 at 11:07, kan liang wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> +	} else if (perf_event_hw_time(event)) {
> +		struct ktime_conv mono;
> +
> +		userpg->cap_user_time_mono_raw = 1;
> +		ktime_get_fast_mono_raw_conv(&mono);

What guarantees that the clocksource used by the timekeeping core is
actually TSC? Nothing at all. You cannot make assumptions here.

Thanks,

        tglx