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Date: Fri, 17 Feb 2012 03:43:11 -0800 From: Paul Turner <pjt@...gle.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: linux-kernel@...r.kernel.org, Venki Pallipadi <venki@...gle.com>, Srivatsa Vaddagiri <vatsa@...ibm.com>, Mike Galbraith <efault@....de>, Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>, Ben Segall <bsegall@...gle.com>, Ingo Molnar <mingo@...e.hu>, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> Subject: Re: [RFC PATCH 01/14] sched: track the runnable average on a per-task entitiy basis On Wed, Feb 15, 2012 at 3:37 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote: > On Wed, 2012-02-01 at 17:38 -0800, Paul Turner wrote: >> + /* >> + * Use 1024us as the unit of measurement since it's a reasonable >> + * approximation of 1ms and fast to compute. >> + */ >> + delta >>= 10; > > ns -> us ?, text talks about ms, slightly confusing Yes, comment was incorrect; I'd noticed this also on a re-read -- it's fixed. > >> + if (!delta) >> + return 0; >> + sa->last_runnable_update = now; >> + >> + delta_w = sa->runnable_avg_period % 1024; > > so delta_w is the chunk of this p we already accounted. > >> + if (delta + delta_w >= 1024) { > > if delta pushes us over 1024*1024 ns (~1ms) we roll a window. > >> + /* period roll-over */ >> + decayed = 1; >> + >> + delta_w = 1024 - delta_w; > > The distance we need to reach the next window. > >> + BUG_ON(delta_w > delta); > > somehow reading this code took forever, this suggests clarification, > either through better variable names or more comments. Could also mean > I'm a moron and should get more sleep or so :-) No... this bit is definitely fiddly, I definitely got it wrong more than once writing it down. And then got it again wrong later when "optimizing" :-). It deserves more comments, I will add. -- 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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