Am 25.09.2012 00:40, schrieb ching: > On 09/24/2012 08:30 PM, Kevin Wolf wrote: >> Am 24.09.2012 13:32, schrieb ching: >>> Hi all, >>> >>> My host is qemu-1.1.1 and x64 kernel 3.5.4. The guest is using aio="native" >>> >>> I am trying to use unsafe cache mode to boost i/o performance. >> aio=native requires the image to be opened with O_DIRECT, i.e. >> cache=none or cache=directsync. If you specify a different cache option, >> it will silently fall back to aio=threads. >> >> Kevin >> > > will qemu log a entry for the silent fallback?
No, that's why it's silent. :-) > Reason: > > I am testing sparse image on btrfs with mount option: > rw,noatime,space_cache,autodefrag,inode_cache > > i encounter a speed difference (around 2X-3X) between > aio=threads,cache=unsafe and aio=native,cache=unsafe > > aio=threads is much faster, i guest there is conflict between "autodefrag" > and linux aio This is odd. The point is that with cache=unsafe it shouldn't even be using Linux AIO in the first place. I can't see why there would be any difference between aio=threads and aio=native with cache=unsafe. Kevin
