Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver
From: Paul E. McKenney <hidden>
Date: 2012-11-14 00:07:41
Also in:
lkml
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:quoted
On 11/13/2012 2:23 PM, Paul E. McKenney wrote:quoted
On Tue, Nov 13, 2012 at 01:39:22PM -0800, Jacob Pan wrote:quoted
On Tue, 13 Nov 2012 13:16:02 -0800 "Paul E. McKenney" [off-list ref] wrote:quoted
quoted
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