linux-kernel - Re: [RFC] sched_clock: Track monotonic raw clock

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Message-ID: <20140722162940.GH3935@laptop>
Date:	Tue, 22 Jul 2014 18:29:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Pawel Moll <pawel.moll@....com>
Cc:	John Stultz <john.stultz@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Baruch Siach <baruch@...s.co.il>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] sched_clock: Track monotonic raw clock

On Tue, Jul 22, 2014 at 05:17:23PM +0100, Pawel Moll wrote:
> > Now, I already mentioned max error bounds, and I've not yet looked at
> > your actual control loop, but that is something to keep in mind, we want
> > something that's limited.
> 
> Indeed. Richard has already expressed concerns that my coefficients
> won't work everywhere (as in with different clock rate ratios) and he's
> most likely right. My money is on a more advanced, "self-tuning"
> solution, where we definitely need an escape condition.

I was wanting to look up software PLLs, as I seem to remember that's
what NTP and PTP use, but Richard should know I think.

Its not really a subject I've looked at before.
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