Am 26.09.2012 01:22, schrieb ching: > 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?
You can attach strace and look for open/pwritev/iosubmit and friends. I did that yesterday with qemu-io and didn't see any iosubmit for 'qemu-io -k -t unsafe'. Kevin
