linux-kernel - Re: [RFC PATCH V2 2/9] perf: Extend ABI to support post-processing monotonic raw conversion

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Date:   Sun, 12 Mar 2023 13:50:15 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     John Stultz <jstultz@...gle.com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        linux-kernel@...r.kernel.org, sboyd@...nel.org, eranian@...gle.com,
        namhyung@...nel.org, adrian.hunter@...el.com
Subject: Re: [RFC PATCH V2 2/9] perf: Extend ABI to support post-processing
 monotonic raw conversion

ersion. So the kernel internal mul/shift information has to be exposed.
> Ugh. Well, I think perf may have made a bad API choice here, so I'm
> still going to push back on exposting timekeeping internals to
> userland.

It's not about the perf ABI.

The perf mmap mult/offset if for PT, which always has raw TSCs.

Without it the PT decoder couldn't supply wall clock time.

-Andi