On Mon, Jul 13, 2009 at 04:40:59PM +0300, Michael S. Tsirkin wrote: > On Mon, Jul 13, 2009 at 04:32:34PM +0300, Gleb Natapov wrote: > > Yeah I understand that other RCU read section may introduce delays too. > > The question is how big the delay may be. > > I recall seeing the number "at least 3 jiffies" somewhere, but that > might have changed since. A grace period lasts a handful of jiffies, depending on kernel configuration and how long readers remain in a given RCU read-side critical section. If a handful of jiffies is too long, there are patches that speed up the grace period, down into the sub-hundred-microsecond range. > > I don't think multiple > > milliseconds delay in device de-assignment is a big issue though. > > Right. My point was that since the sync is done under kvm lock, the > guest can easily get blocked trying to get kvm lock meanwhile. I will ask the usual question -- can call_rcu() be used to move the grace period out from under the lock? (Often this can be done, but not always.) Thanx, Paul -- 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
