On Wed, Apr 19, 2017 at 08:37:03AM -0700, Paul E. McKenney wrote: > On Wed, Apr 19, 2017 at 03:15:53PM +0200, Peter Zijlstra wrote: > > On Wed, Apr 19, 2017 at 06:02:45AM -0700, Paul E. McKenney wrote: > > > On Wed, Apr 19, 2017 at 01:28:45PM +0200, Peter Zijlstra wrote: > > > > > > > > So the thing Maz complained about is because KVM assumes > > > > synchronize_srcu() is 'free' when there is no srcu_read_lock() activity. > > > > This series 'breaks' that. > > > > > > > > I've not looked hard enough at the new SRCU to see if its possible to > > > > re-instate that feature. > > > > > > And with the fix I gave Maz, the parallelized version is near enough > > > to being free as well. It was just a stupid bug on my part: I forgot > > > to check for expedited when scheduling callbacks. > > > > Right, although for the old SRCU it was true for !expedited as well. > > Which is all good fun until someone does a call_srcu() on each and > every munmap() syscall. ;-)
Well, that being a different SRCU domain doesn't affect the KVM memslot domain thingy ;-) > But the current code is much better housebroken. ;-) It is. But a workload that manages to hit sync_expedited in a loop on all CPUs is still O(n^2) work. And the more sync_expedited instances we have, the more likely that becomes.
