On Tue, 10 Apr 2012 13:39:14 +0300 Avi Kivity <avi@xxxxxxxxxx> wrote: > On 04/09/2012 10:46 PM, Marcelo Tosatti wrote: > > Perhaps the mmu_lock hold times by get_dirty are a large component here? > > If that can be alleviated, not only RO->RW faults benefit. > > > > > > Currently the longest holder in normal use is probably reading the dirty > log and write protecting the shadow page tables. > > We could fix that by switching to O(1) write protection > (write-protecting PML4Es instead of PTEs). It would be interesting to > combine O(1) write protection with lockless write-enabling. > As Marcelo suggested during reviewing srcu-less dirty logging, we can mitigate the get_dirty's mmu_lock hold time problem cleanly, locally in get_dirty_log(), by using cond_resched_lock() -- although we need to introduce cond_rescheck_lock_cb() to conditionally flush TLB. I have already started that work. Actually I introduced rmap based get_dirty for that kind of fine-grained contention control. I think we should do our best not to affect mmu so much just for the limited time of live migration. Takuya -- 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
