On 09/25/2012 09:33 PM, Kevin Wolf wrote: > 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 >
is it possible to check the open mode of file and whether it is using aio at runtime?