On Tue, Nov 15, 2011 at 11:47:58AM +0100, ext Juan Quintela wrote: > Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> wrote: > > Adding qemu-devel ML to CC. > > > > Your question should have been sent to qemu-devel ML because the logic > > is implemented in QEMU, not KVM. > > > > (2011/11/11 1:35), Oliver Hookins wrote: > >> Hi, > >> > >> I am performing some benchmarks on KVM migration on two different types of VM. > >> One has 4GB RAM and the other 32GB. More or less idle, the 4GB VM takes about 20 > >> seconds to migrate on our hardware while the 32GB VM takes about a minute. > >> > >> With a reasonable amount of memory activity going on (in the hundreds of MB per > >> second) the 32GB VM takes 3.5 minutes to migrate, but the 4GB VM never > >> completes. Intuitively this tells me there is some watermarking of dirty pages > >> going on that is not particularly efficient when the dirty pages ratio is high > >> compared to total memory, but I may be completely incorrect. > > > You can change the ratio IIRC. > > Hopefully, someone who knows well about QEMU will tell you better ways. > > > > Takuya > > > >> > >> Could anybody fill me in on what might be going on here? We're using libvirt > >> 0.8.2 and kvm-83-224.el5.centos.1 > > This is pretty old qemu/kvm code base. > In principle, it makes no sense that with 32GB RAM migration finishes, > and with 4GB RAM it is unable (intuitively it should be, if ever, the > other way around). If the syncing of dirty pages is based on some kind of ratio that causes it to resync everything if more than a certain percentage of total pages are dirty then this could explain it, as with a smaller amount of memory it could be continually restarting. I can certainly state from observation that the network traffic continues at high speed the whole time so perhaps this makes some sense. I was hoping that this behaviour would cause someone to recall a problem like this that was solved - maybe this is not the case! > > Do you have an easy test that makes the problem easily reproducible? > Have you tried ustream qemu.git? (some improvements on that department). I haven't just yet, but I'll give this a try. Thanks for the suggestion! -- 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
