On Thursday, August 23, 2007 12:27 am Benjamin Herrenschmidt wrote: > > Of course, the normal memory barrier would usually be a > > "spin_unlock()" or something like that, not a "wmb()". In fact, I > > don't think the powerpc implementation (as an example of this) will > > actually synchronize with anything *but* a spin_unlock(). > > We are even more sneaky in the sense that we set a per-cpu flag on > any MMIO write and do the sync automatically in spin_unlock() :-) Yeah, that's a reasonable thing to do, and in fact I think there's code to do something similar when a task is switched out (this keeps user level drivers from having do mmiowb() type things). FWIW, I think I had an earlier version of the patch that used the name pioflush() or something similar, the only confusing thing about that name is that the primitive doesn't actually force I/Os down to the device level, just to the closest bridge. It'll be interesting to see if upcoming x86 designs share this problem (e.g. large HT or CSI topologies). Jesse - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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