Messages in this thread | | | Date | Thu, 30 Oct 2008 13:23:23 -0700 | From | Suresh Siddha <> | Subject | Re: [patch] generic-ipi: fix the smp_mb() placement |
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On Thu, Oct 30, 2008 at 11:53:22AM -0700, Ingo Molnar wrote: > > * Suresh Siddha <suresh.b.siddha@intel.com> wrote: > > > Subject: generic-ipi: fix the smp_mb() placement > > > > smp_mb() is needed (to make the memory operations visible globally) > > before sending the ipi on the sender and the receiver (on Alpha > > atleast) needs smp_read_barrier_depends() in the handler before > > reading the call_single_queue list in a lock-free fashion. > > > > On x86, x2apic mode register accesses for sending IPI's don't have > > serializing semantics. So the need for smp_mb() before sending the > > IPI becomes more critical in x2apic mode. > > > > Remove the unnecessary smp_mb() in csd_flag_wait(), as the presence > > of that smp_mb() doesn't mean anything on the sender, when the ipi > > receiver is not doing any thing special (like memory fence) after > > clearing the CSD_FLAG_WAIT. > > nice! Did you see an actual lockup due to this?
We didn't see the lockup in our tests but Xen folks reported similar failures with their smp call function code.
> Seems like a v2.6.28 fix to me in any case.
Yes.
thanks, suresh
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