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, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>