From: Peter Zijlstra <peterz@infradead.org>
To: John Stultz <jstultz@google.com>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
mingo@redhat.com, linux-kernel@vger.kernel.org, sboyd@kernel.org,
eranian@google.com, namhyung@kernel.org, ak@linux.intel.com,
adrian.hunter@intel.com
Subject: Re: [RFC PATCH V2 2/9] perf: Extend ABI to support post-processing monotonic raw conversion
Date: Tue, 14 Feb 2023 11:43:33 +0100 [thread overview]
Message-ID: <Y+tl1ZJiWuMeKCnB@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CANDhNCq1b-7C=cox6ufC3Kxycu87qPzDHtJH_5jwPmPjjig5ww@mail.gmail.com>
On Mon, Feb 13, 2023 at 02:22:39PM -0800, John Stultz wrote:
> The interpoloation is pretty easy to do:
>
> do {
> start= readtsc();
> clock_gett(CLOCK_MONOTONIC_RAW, &ts);
> end = readtsc();
> delta = end-start;
> } while (delta > THRESHOLD) // make sure the reads were not preempted
> mid = start + (delta +(delta/2))/2; //round-closest
>
> and be able to get you a fairly close matching of TSC to
> CLOCK_MONOTONIC_RAW value.
>
> Once you have that mapping you can take a few samples and establish
> the linear function.
Right, this is how we do the TSC calibration in the first place, and if
NTP can achieve high correctness over a network, then surely we can do
better locally.
That is, this scheme should work for all CLOCKs, not only MONOTONIC_RAW.
next prev parent reply other threads:[~2023-02-14 15:57 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-13 19:07 [RFC PATCH V2 0/9] Convert TSC to monotonic raw clock for PEBS kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 1/9] timekeeping: Expose the conversion information of monotonic raw kan.liang
2023-02-13 19:28 ` John Stultz
2023-02-13 19:07 ` [RFC PATCH V2 2/9] perf: Extend ABI to support post-processing monotonic raw conversion kan.liang
2023-02-13 19:37 ` John Stultz
2023-02-13 21:40 ` Liang, Kan
2023-02-13 22:22 ` John Stultz
2023-02-14 10:43 ` Peter Zijlstra [this message]
2023-02-14 17:46 ` Liang, Kan
2023-02-14 19:37 ` John Stultz
2023-02-14 20:09 ` Liang, Kan
2023-02-14 20:21 ` John Stultz
2023-03-12 20:50 ` Andi Kleen
2023-02-14 19:34 ` John Stultz
2023-02-14 14:51 ` Liang, Kan
2023-02-14 17:00 ` Liang, Kan
2023-02-14 20:11 ` John Stultz
2023-02-14 20:38 ` Liang, Kan
2023-02-17 23:11 ` John Stultz
2023-03-08 18:44 ` Liang, Kan
2023-03-09 1:17 ` John Stultz
2023-03-09 16:56 ` Liang, Kan
2023-03-11 5:55 ` John Stultz
2023-03-13 21:19 ` Liang, Kan
2023-03-18 6:02 ` John Stultz
2023-03-21 15:26 ` Liang, Kan
2023-02-14 19:52 ` John Stultz
2023-02-13 19:07 ` [RFC PATCH V2 3/9] perf/x86: Factor out x86_pmu_sample_preload() kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 4/9] perf/x86: Enable post-processing monotonic raw conversion kan.liang
2023-02-14 20:02 ` Thomas Gleixner
2023-02-14 20:21 ` Liang, Kan
2023-02-14 20:55 ` Thomas Gleixner
2023-03-21 15:38 ` Liang, Kan
2023-02-13 19:07 ` [RFC PATCH V2 5/9] perf/x86/intel: Enable large PEBS for monotonic raw kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 6/9] tools headers UAPI: Sync linux/perf_event.h with the kernel sources kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 7/9] perf session: Support the monotonic raw clock conversion information kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 8/9] perf evsel, tsc: Support the monotonic raw clock conversion kan.liang
2023-02-13 19:07 ` [RFC PATCH V2 9/9] perf evsel: Enable post-processing monotonic raw conversion by default kan.liang
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