Messages in this thread | | | Subject | Re: [patch 1/3] sched: init rt_avg stat whenever rq comes online | From | Suresh Siddha <> | Date | Wed, 18 Aug 2010 17:20:13 -0700 |
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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
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