Re: [Qemu-devel] linux aio and cache mode

[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?


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

ching