Messages in this thread | | | Subject | Re: [RFC PATCH 02/15] nohz_task: Avoid nohz task cpu as non-idle timer target | From | Peter Zijlstra <> | Date | Tue, 21 Dec 2010 08:50:47 +0100 |
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On Tue, 2010-12-21 at 01:13 +0100, Frederic Weisbecker wrote: > On Mon, Dec 20, 2010 at 04:47:58PM +0100, Peter Zijlstra wrote: > > On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote: > > > Unbound timers are preferably targeted for non idle cpu. If > > > possible though, prioritize idle cpus over nohz task cpus, > > > because the main point of nohz task is to avoid unnecessary > > > timer interrupts. > > > > Oh is it? > > > > I'd very much expect the cpu that arms the timer to get the interrupt. I > > mean, if the task doesn't want to get interrupted by timers, > > _DON'T_USE_TIMERS_ to begin with. > > > > So no, don't much like this at all. > > I suspect TIMER_NOT_PINNED has been introduced to save some power by > avoiding to wake up idle cpus. > > This is used by mod_timer(), schedule_timeout(), mod_timer_pending() > So that's widely used and removing that could have a deep impact on > power.
Yeah so? Who said task_nohz had to have the bestest power savings around? Its not a laptop feature by any means. Simply disable the thing: echo 0 > /proc/sys/kernel/timer_migration, or better yet, teach it about your cpuset constraints and avoid it migrating timers into your set and keep timers pinned within the set.
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