On 04/26/2016 07:45 PM, Tejun Heo wrote: > 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. > ^^^ Ah. Time warp. I knew it would happen eventually :-)
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