I still haven't had the chance to test this properly. (server is in production), but the problem manifested itself by accident. So, here's a little bit of information.
I started downloading (rsync) a qcow image from the file server and noticed it was bit slow. 14MB/sec max - 790kB/s after a while. This is writing to a simple single sata disk. Then the virtual machines started to become unresponsive and I had to interrupt the download, or the server would have gone down. It's not memory pressure. Memory was at +/- 900MB (of 8GB). Only 2 small virtual machines were running, BUT there was a snapshot present. It's not qemu-img that causes the panics. Any I/O will do it. Then the famous messages start appearing in kern.log: [149164.740056] INFO: task kvm:21354 blocked for more than 120 seconds. [149164.740294] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [...] [149164.740595] [<ffffffff8155d557>] __mutex_lock_slowpath+0x107/0x190 Restarting the download without lvm snapshot present yields: - 11MB/s, but more or less constant. - Running virtual machines are responsive as ever - No errors in kern.log -- You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to qemu-kvm in Ubuntu. https://bugs.launchpad.net/bugs/712392 Title: qemu-img convert blocks other tasks -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs
