Messages in this thread | | | Date | Wed, 6 Jun 2012 08:49:45 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi |
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On Wed, Jun 06, 2012 at 08:23:54AM -0700, Arjan van de Ven wrote: > On 6/6/2012 7:41 AM, Paul E. McKenney wrote: > > On Wed, Jun 06, 2012 at 10:43:43AM +0200, Peter Zijlstra wrote: > >> On Tue, 2012-06-05 at 15:12 -0700, Paul E. McKenney wrote: > >>>> What I can't see is the isolated functional, aside from the above > >>>> mentioned things, that's not strictly a per-cpu property, we can have a > >>>> group that's isolated from the rest but not from each other. > >>> > >>> I suspect that Thomas is thinking that the CPU is so idle that it no > >>> longer has to participate in TLB invalidation or RCU. (Thomas will > >>> correct me if I am confused.) But Peter, is that the level of idle > >>> you are thinking of? > >> > >> No, we're talking about isolated, so its very much running something. > > > > From what I can see, if the CPU is running something, this is Thomas's > > "Isolated functional" state rather than his "Isolated idle" state. > > The isolated-idle state should not need to participate in TLB invalidation > > or RCU, so that the CPU never ever needs to wake up while in the > > isolated-idle state. > > btw TLB invalidation I think is a red herring in this discussion > (other than "global PTEs" kind of kernel pte changes); > at least on x86 this is not happening for a long time; if a CPU is > really idle (which means the CPU internally flushes the tlbs anyway), > Linux also switches to the kernel PTE set so there's no need for a flush > later on.
Right, as I understand it, only unmappings in the kernel address space would need to IPI an idle CPU. But this is still a source of IPIs that could wake up the CPU, correct?
Thanx, Paul
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