Messages in this thread | | | Date | Wed, 31 Aug 2011 00:44:06 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 12/32] nohz: Try not to give the timekeeping duty to a cpuset nohz cpu |
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On Tue, Aug 30, 2011 at 05:37:28PM +0200, Peter Zijlstra wrote: > On Tue, 2011-08-30 at 17:17 +0200, Frederic Weisbecker wrote: > > On Mon, Aug 29, 2011 at 04:55:45PM +0200, Peter Zijlstra wrote: > > > On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote: > > > > Try to give the timekeeing duty to a CPU that doesn't belong > > > > to any nohz cpuset when possible, so that we increase the chance > > > > for these nohz cpusets to run their CPUs out of periodic tick > > > > mode. > > > > > > You and Dmitiri might want to get together: > > > > > > lkml.kernel.org/r/20110823195628.GB4533@sgi.com > > > > Right! > > > > There is another missing piece in my patchset. If every non adaptive-nohz > > CPUs are sleeping, then none is handling the do_timer duty and adaptive nohz > > CPUs run with a stale jiffies and walltime. > > Doesn't nohz already deal with the case of all cpus being idle? In that > case the cpu that wakes up first gets to play catch up on irq_enter() or > so.
Sure and that works for the nohz idle case. But that's not enough anymore in the case of adaptive nohz CPUs. They can run for a while without the tick and if nobody else maintains a tick either then jiffies and walltime are not maintained anymore.
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