On Thu, Jan 09, 2020 at 11:17:42AM -0500, Peter Xu wrote: > On Thu, Jan 09, 2020 at 10:59:50AM -0500, Michael S. Tsirkin wrote: > > On Thu, Jan 09, 2020 at 09:57:08AM -0500, Peter Xu wrote: > > > Branch is here: https://github.com/xzpeter/linux/tree/kvm-dirty-ring > > > (based on kvm/queue) > > > > > > Please refer to either the previous cover letters, or documentation > > > update in patch 12 for the big picture. > > > > I would rather you pasted it here. There's no way to respond otherwise. > > Sure, will do in the next post. > > > > > For something that's presumably an optimization, isn't there > > some kind of testing that can be done to show the benefits? > > What kind of gain was observed? > > Since the interface seems to settle soon, maybe it's time to work on > the QEMU part so I can give some number. It would be interesting to > know the curves between dirty logging and dirty ring even for some > small vms that have some workloads inside. > > > > > I know it's mostly relevant for huge VMs, but OTOH these > > probably use huge pages. > > Yes huge VMs could benefit more, especially if the dirty rate is not > that high, I believe. Though, could you elaborate on why huge pages > are special here? > > Thanks, With hugetlbfs there are less bits to test: e.g. with 2M pages a single bit set marks 512 pages as dirty. We do not take advantage of this but it looks like a rather obvious optimization. > -- > Peter Xu
