Messages in this thread | | | Date | Tue, 10 Jan 2012 22:19:36 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken |
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* Arjan van de Ven <arjan@linux.intel.com> [2012-01-10 06:32:16]:
> On 1/10/2012 1:18 AM, Ingo Molnar wrote: > > > > * Suresh Siddha <suresh.b.siddha@intel.com> wrote: > > > >> On Tue, 2012-01-10 at 00:58 -0500, Youquan Song wrote: > >>> Thanks Peter! Here is the patch. > >> > >> Youquan, As far as I know both the > >> sched_smt_power_savings/sched_mc_power_savings are broken for atleast an > >> year. > > > > We want a single knob, sched_power_savings - with the mc_ and > > smt_ ones still kept and aliased to sched_power_savings, for > > compatibility reasons. > > > > As Peter said, the other reasonable option is to have no knob at > > all and restart this code from scratch. > > > > The other thing we should do is to add sane defaults: to turn on > > sched_power_savings *AUTOMATICALLY* when a system is obviously > > battery driven and turn it off when the system is obviously AC > > driven. User-space can still implement policy and override the > > kernel's default, but there's absolutely no excuse to not offer > > this default ourselves. > > a very good default would be to keep all tasks on one package until half > the cores in the package are busy, and then start spreading out. > > I suspect that'll be the 90% case coverage.
This is a good default, but I guess we will not consolidate tasks into SMT threads by default since that will be a larger performance drop.
--Vaidy
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