Messages in this thread | | | Date | Thu, 30 Oct 2008 19:53:22 +0100 | From | Ingo Molnar <> | Subject | Re: [patch] generic-ipi: fix the smp_mb() placement |
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* 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? Seems like a v2.6.28 fix to me in any case.
Ingo
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