On Tue, 2010-06-01 at 21:36 +0200, Andi Kleen wrote: > > Collecting the contention/usage statistics on a per spinlock > > basis seems complex. I believe a practical approximation > > to this are adaptive mutexes where upon hitting a spin > > time threshold, punt and let the scheduler reconcile fairness. > > That would probably work, except: how do you get the > adaptive spinlock into a paravirt op without slowing > down a standard kernel? It only ever comes into play in the case where the spinlock is contended anyway -- surely it shouldn't be _that_ much of a performance issue? See the way that ppc64 handles it -- on a machine with overcommitted virtual cpus, it will call __spin_yield (arch/powerpc/lib/locks.c) on contention, which may cause the virtual CPU to donate its hypervisor timeslice to the vCPU which is actually holding the lock in question. -- David Woodhouse Open Source Technology Centre David.Woodhouse@xxxxxxxxx Intel Corporation -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
