linux-kernel - Re: [PATCH v4 1/4] Produce system time from correlated clocksource

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Message-ID: <20151020085408.GA2542@netboy>
Date:	Tue, 20 Oct 2015 10:54:08 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Christopher Hall <christopher.s.hall@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>, kevin.b.stanton@...el.com
Subject: Re: [PATCH v4 1/4] Produce system time from correlated clocksource

On Mon, Oct 19, 2015 at 05:36:56PM -0700, John Stultz wrote:
> If we're only tracking 4ms of history, how does this solution
> measurably improve the error over using the timestamps to generate
> MONOTONIC_RAW clock deltas (which doesn't require keeping any history)
> and using getnstime_raw_and_real to take an anchor point to calculate
> the delta from?  Why is adding complexity necessary?

This idea is variant of what I suggested in another reply in this
thread.  To my understanding, there is no need at all to keep a
history arbitrarily 4 ms long.  Instead, the DSP driver (or whoever
else may need such a thing) can simply sample the system time at the
rate needed for that particular application.

Thanks,
Richard
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