On 11/12/2010 02:17 PM, Jeremy Fitzhardinge wrote: > On 11/12/2010 02:12 PM, H. Peter Anvin wrote: >> On 11/03/2010 07:59 AM, Jeremy Fitzhardinge wrote: >>> - with an unmodified struct spinlock, it can check to see if >>> head == tail after unlock; if not, then there's someone else >>> trying to lock, and we can do a kick. Unfortunately this >>> generates very high level of redundant kicks, because the >>> waiting CPU might not have blocked yet (which is the common >>> case) >>> >> How high is "very high" here -- most of the time (so that any mitigation >> on the slow patch is useless)? > > I'll need to remeasure, but I think around 90% of the slowpath entries > were spurious without this. In other words, when spinlocks do contend, > most of the time it isn't very serious and the other cpu doesn't spend > much time spinning. > 90% of the slowpath entries is one thing, my real question is the fraction of fastpath entries that get diverted to the slowpath. It affects where mitigation needs to happen. -hpa _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
