08.04.2010 09:07, Thomas Mueller wrote: []
This helped alot: I enabled "deadline" block scheduler instead of the default "cfq" on the host system. tested with: Host Debian with scheduler deadline, Guest Win2008 with Virtio and cache=none. (26MB/s to 50MB/s boost measured) Maybe this is also true for Linux/Linux. I expect that scheduler "noop" for linux guests would be good.
Hmm. I wonder why it helped. In theory, host scheduler should not change anything for cache=none case, at least for raw partitions of LVM volumes. This is because with cache=none, the virtual disk image is opened with O_DIRECT flag, which means all I/O bypasses host scheduler and buffer cache. I tried a few quick tests here, -- with LVM volumes it makes no measurable difference. But if the guest disk images are on plain files (also raw), scheduler makes some difference, and indeed deadline works better. Maybe you were testing with plain files instead of block devices? Thanks! /mjt -- 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
