Messages in this thread | | | Date | Tue, 30 Aug 2011 00:53:19 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 04/32] nohz: Separate idle sleeping time accounting from nohz switching |
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On Mon, Aug 29, 2011 at 07:44:01PM +0200, Peter Zijlstra wrote: > On Mon, 2011-08-29 at 18:32 +0200, Frederic Weisbecker wrote: > > On Mon, Aug 29, 2011 at 04:23:19PM +0200, Peter Zijlstra wrote: > > > On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote: > > > > To prepare for having nohz mode switching independant from idle, > > > > pull the idle sleeping time accounting out of the tick stop API. > > > > > > > > This implies to implement some new API to call when we > > > > enter/exit idle. > > > > > > I mean, I really love brevity, but you seem to just not state all the > > > important bits ;-) > > > > > > So the goal is to disable the tick more often (say when running 1 > > > userbound task), why does that need new hooks? If we already had the > > > tick disabled, the tick_nohz_stop_sched_tick() call on going idle will > > > simply not do anything. > > > > > > If we go from idle to running something we want to enable the tick > > > initially because doing the task wakeup involves RCU etc.. Once we find > > > the task is indeed userbound and we've finished all our state we can > > > disable the thing again. > > > > That's because we are going to have two different sources of stop/restarting > > the tick: either idle or a random task. In the case of idle we have very > > specific things to handle like idle time accounting, idle stats, rcu, ... > > > > I could do these things conditionally using a some idle_cpu() checks but > > the end result would not be very proper. > > Right, but you didn't explain any of that in the changelog. So the > reasoning is that because tick_nohz_stop_sched_tick() does more than > just stop the tick, and this extra work needs to be isolated to just the > idle case, therefore we need hooks specific for the idle loop.
Right, I'll update the changelog.
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