Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver | Date | Wed, 14 Nov 2012 00:02 +0100 |
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On Tuesday, November 13, 2012 02:45:11 PM Arjan van de Ven wrote: > On 11/13/2012 2:23 PM, Paul E. McKenney wrote: > > On Tue, Nov 13, 2012 at 01:39:22PM -0800, Jacob Pan wrote: > >> On Tue, 13 Nov 2012 13:16:02 -0800 > >> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > >> > >>>> Please refer to Documentation/thermal/intel_powerclamp.txt for more > >>>> details. > >>> > >>> If I read this correctly, this forces a group of CPUs into idle for > >>> about 600 milliseconds at a time. This would indeed delay grace > >>> periods, which could easily result in user complaints. Also, given > >>> the default RCU_BOOST_DELAY of 500 milliseconds in kernels enabling > >>> RCU_BOOST, you would see needless RCU priority boosting. > >>> > >> the default idle injection duration is 6ms. we adjust the sleep > >> interval to ensure idle ratio. So the idle duration stays the same once > >> set. So would it be safe to delay grace period for this small amount in > >> exchange for less over head in each injection period? > > > > Ah, 6ms of delay is much better than 600ms. Should be OK (famous last > > words!). > > well... power clamping is not "free". > You're going to lose performance as a trade off for dropping instantaneous power consumption....
Yes. It is good to realize that when the clamping triggers, we already have some more to worry about than losing some performance. :-)
The problem here is to find a way to lose as little performance as we possibly can and prevent the system from overheating at the same time.
Thanks, Rafael
-- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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