Hello, Peter. On Tue, Apr 26, 2016 at 10:27:59AM -0700, Peter Hurley wrote: > > It's unlikely to make any measureable difference. Is xchg() actually > > cheaper than store + rmb? > > store + mfence (full barrier), yes. Roughly 2x faster. > > https://lkml.org/lkml/2015/11/2/607 Ah, didn't know that. Thanks for the pointer. > > I'm not necessarily against making all clearings of > > PENDING to be followed by a rmb or use xhcg. Reasons 2-4 are pretty > > weak tho. > > I agree 2 and 3 are not the best reasons. > Actually, it looks that I'm in the minority anyway, and that style-wise, > naked barrier is preferred. As long as what's happening is clearly documented, I think either is fine. I'm gonna go with Roman's mb patch for -stable fix but think it'd be nice to have a separate patch to consolidate the paths which clear PENDING and make them use xchg. If you can spin up a patch for that, I'd be happy to apply it to wq/for-3.7. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
