Messages in this thread | | | Date | Thu, 9 Feb 2012 16:52:49 +0100 | From | Frederic Weisbecker <> | Subject | Re: [v7 0/8] Reduce cross CPU IPI interference |
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On Thu, Feb 02, 2012 at 10:29:57AM -0600, Christoph Lameter wrote: > On Thu, 2 Feb 2012, Frederic Weisbecker wrote: > > > > Some pinned timers might be able to get special treatment as well - take for > > > example the vmstat work being schedule every second, what should we do with > > > it for CPU isolation? > > > > Right, I remember I saw these vmstat timers on my way when I tried to get 0 > > interrupts on a CPU. > > > > I think all these timers need to be carefully reviewed before doing anything. > > But we certainly shouldn't adopt the behaviour of migrating timers by default. > > > > Some timers really needs to stay on the expected CPU. Note that some > > timers may be shutdown by CPU hotplug callbacks. Those wouldn't be migrated > > in case of CPU offlining. We need to keep them. > > > > > It makes sense to me to have that stop scheduling itself when we have the tick > > > disabled for both idle and a nohz task. > > The vmstat timer only makes sense when the OS is doing something on the > processor. Otherwise if no counters are incremented and the page and slab > allocator caches are empty then there is no need to run the vmstat timer.
So this is a typical example of a timer we want to shutdown when the CPU is idle but we want to keep it running when we run in adaptive tickless mode (ie: shutdown the tick while the CPU is busy). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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