On Wed, Jun 29, 2011 at 1:21 PM, Alexander Graf <ag...@suse.de> wrote: > On 29.06.2011, at 13:59, Kevin Wolf wrote: >> I'm not entirely sure if I should suggest writeback or none as the new >> default, but I think it could make sense to change it. > > None as default would be a bad choice, as not all underlying file systems > support it. Try cache=none on tmpfs or nfs. It will just fail on you. > What I'd personally like to see is some sort of detection that can determine > which caching mode would perform best. So it would do cache=none when it > makes sense (raw block device), otherwise cache=writeback.
O_DIRECT works on the Linux NFS client. The performance currently isn't great with vectored I/O (which QEMU does) but there is work ongoing to improve it. Your point makes sense though. The default (no explicit cache=) should mean "the most appropriate caching mode". Stefan
