From: ching <lsching17@gmail.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] linux aio and cache mode
Date: Tue, 25 Sep 2012 06:40:07 +0800 [thread overview]
Message-ID: <5060E147.3080306@gmail.com> (raw)
In-Reply-To: <5060524C.2070509@redhat.com>
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
next prev parent reply other threads:[~2012-09-24 22:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-24 11:32 [Qemu-devel] linux aio and cache mode ching
2012-09-24 12:30 ` Kevin Wolf
2012-09-24 22:40 ` ching [this message]
2012-09-25 13:33 ` Kevin Wolf
2012-09-25 23:22 ` ching
2012-09-26 7:51 ` Kevin Wolf
2012-09-28 0:00 ` ching
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