On Wed, 18 Feb 2009, Ingo Molnar wrote: > > an off-list comment pointed out this piece of information as > well: > > http://www.sandpile.org/ia32/coherent.htm > > A WRMSR to one of the x2APIC MSRs (0000_0800h...0000_0BFFh) is > not guaranteed to be serializing. > > So i suspect we should just enclose it in smp_mb() pairs to make > sure it's a full barrier in both directions? Why would we care about "both directions"? I think putting an sfence _before_ the wrmsr (and not even all of them - just put it in front of the "send IPI" sequence) should be fine. Any other ordering sounds like just unnecessary overhead to me. We do want this to be low-overhead, even if we probably don't care _that_ much. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
