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Message-ID: <20140719050233.GA4408@netboy> Date: Sat, 19 Jul 2014 07:02:33 +0200 From: Richard Cochran <richardcochran@...il.com> To: Pawel Moll <pawel.moll@....com> Cc: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, Andy Lutomirski <luto@...capital.net>, John Stultz <john.stultz@...aro.org>, Stephen Boyd <sboyd@...eaurora.org>, Baruch Siach <baruch@...s.co.il>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org Subject: Re: [RFC] sched_clock: Track monotonic raw clock On Fri, Jul 18, 2014 at 06:43:39PM +0100, Pawel Moll wrote: > > This code definitely needs more work and testing (I'm not 100% > sure if the Kp and Ki I've picked for the proportional and > integral terms are universal), I wouldn't bet on it. > but for now wanted to see > if this approach makes any sense whatsoever. You are reading sched_clock and mono-raw together every so often. Really stupid question: Why not just place that information into the trace buffer and let user space do the clock correction? ... > + /* Tune the cyc_to_ns formula */ > + mult_adj = sign * (error >> 2) + (cd.error_int >> 2); So Kp = Ki = 0.25? And did you say that the sample rate is 10/second? I guess that, while this works well on your machine, it might not always do so, depending on the mono-raw clock. Probably Kp/i need to be tunable to a particular system. Even better would be to leave this out of the kernel altogether. Thanks, Richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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