Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 13 Nov 2012 16:03:39 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver |
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On Wed, Nov 14, 2012 at 12:02:00AM +0100, Rafael J. Wysocki wrote: > 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.
Understood. My concern is in-kernel confusion rather than performance.
Thanx, Paul
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