On Wed, Apr 14, 2010 at 7:04 AM, Dor Laor <[email protected]> wrote: > On 04/13/2010 05:33 PM, Bill McGonigle wrote: >> Hi, all, >> >> The subject line is a bit of a guess. I'm running the preview release >> on an updated F12, with a Vista guest (no virtio drivers yet) and after >> an initial OS install the software updates have been running for a bit >> more than 12 hours, and the system's hard drives have been thrashing >> heartily during it. >> >> I've got a data-journaled ext4 on luks on raid-1. That's clearly not a >> write-optimized stack, but performance has been pretty good in the past >> with KVM& Vista and fine for normal system operations. If I check out >> iotop while it's thrashing it's all in [jbd2/dm-2-8] and [kdmflush]. >> >> Looking for the blocked tasks (below), I think I see kvm is >> fdatasync'ing, on what I'd presume is a very frequent basis. I noticed >> that fsync was replaced with fdatasync not too long ago, but that should >> have helped performance, not clobbered it (I think...). Ideally I could > > Adding Christoph who has done the change. > Do you use cache=off or writethrough? > >> tell kvm to fdatasync every 5 seconds or something like that and get >> batched writes. I've tried switching schedules to cfq, deadline, and >> noop, with no big difference. >> >> Does this seem sensible or am I totally off-base here? I'm rebuilding >> this virtual machine after a virtio driver install went south, so I'd >> like to at least have a usable solution (but not libeatmydata) without >> them. I also run OS's with no virtio driver support at times. >>
Not sure if it's related but I've been seeing very poor IO performance for guests on a fairly new F12 system. It doesn't seem to make a difference whether the guests are Linux or Windows. For instance, an XP installation is running right now and qemu-kvm is struggling along only occasionally writing around 35KB/s, according to iotop. A Centos 5.4 installation I did last week was also somewhat hamstrung by poor virtual disk performance. In both cases this is with image files rather than logical volumes. I know the latter if preferable but I haven't seen this kind of slowdown with image files before. Adam _______________________________________________ virt mailing list [email protected] https://admin.fedoraproject.org/mailman/listinfo/virt
