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Date: Wed, 18 Aug 2010 17:20:13 -0700 From: Suresh Siddha <suresh.b.siddha@...el.com> To: Peter Zijlstra <peterz@...radead.org> Cc: "mingo@...e.hu" <mingo@...e.hu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "chris@...stnet.net" <chris@...stnet.net>, "debian00@...ceadsl.fr" <debian00@...ceadsl.fr>, "hpa@...or.com" <hpa@...or.com>, "jonathan.protzenko@...il.com" <jonathan.protzenko@...il.com>, "mans@...sr.com" <mans@...sr.com>, "psastudio@...l.ru" <psastudio@...l.ru>, "rjw@...k.pl" <rjw@...k.pl>, "stephan.eicher@....de" <stephan.eicher@....de>, "sxxe@....de" <sxxe@....de>, "thomas@...hlinux.org" <thomas@...hlinux.org>, "venki@...gle.com" <venki@...gle.com>, "wonghow@...il.com" <wonghow@...il.com>, "stable@...nel.org" <stable@...nel.org>, tglx <tglx@...utronix.de> Subject: Re: [patch 1/3] sched: init rt_avg stat whenever rq comes online On Tue, 2010-08-17 at 01:51 -0700, Peter Zijlstra wrote: > On Mon, 2010-08-16 at 21:25 +0200, Peter Zijlstra wrote: > > You can use something like: > > > > suspend: > > __get_cpu_var(cyc2ns_suspend) = sched_clock(); > > > > resume: > > for_each_possible_cpu(i) > > per_cpu(cyc2ns_offset, i) += per_cpu(cyc2ns_suspend); > > > > or something like that to keep sched_clock() stable, which is exactly > > what most (all?) its users expect when we report the TSC is usable. > > That's actually broken, you only want a single offset, otherwise we > de-sync the TSC, which is bad. > > So simply store the sched_clock() value at suspend time on the single > CPU that is still running, then on resume make sure sched_clock() > continues there by adding that stamp to all CPU offsets. Peter, That might not be enough. I should add that in my Lenovo T410 (having 2 core wsm cpu), TSC's are somehow set to a strange big value (for example 0xfffffffebc22f02e) after resume from S3. It looks like bios might be writing TSC during resume. I am not sure if this is the case for other OEM laptops aswell. I am checking. So such large values of TSC (leading to a very big difference between rq->clock and rq->age_stamp) wont be correctly handled by scale_rt_power() either. thanks, suresh -- 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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