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Re: [Qemu-devel] Default cache mode
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 16:05:22 +0200 |
On 29.06.2011, at 15:57, Stefan Hajnoczi wrote:
> On Wed, Jun 29, 2011 at 1:21 PM, Alexander Graf <address@hidden> wrote:
>> On 29.06.2011, at 13:59, Kevin Wolf wrote:
>>> I'm not entirely sure if I should suggest writeback or none as the new
>>> default, but I think it could make sense to change it.
>>
>> None as default would be a bad choice, as not all underlying file systems
>> support it. Try cache=none on tmpfs or nfs. It will just fail on you.
>> What I'd personally like to see is some sort of detection that can determine
>> which caching mode would perform best. So it would do cache=none when it
>> makes sense (raw block device), otherwise cache=writeback.
>
> O_DIRECT works on the Linux NFS client. The performance currently
> isn't great with vectored I/O (which QEMU does) but there is work
> ongoing to improve it.
It does? One of the things I stumbled over when doing autotest was that
cache=none was the default - and that simply failed on my nfs-root system.
> Your point makes sense though. The default (no explicit cache=)
> should mean "the most appropriate caching mode".
Yeah, that's what defaults should be like in most cases. The same reason people
are for going with -cpu host as default :).
Alex
- Re: [Qemu-devel] Default cache mode, (continued)
Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
Re: [Qemu-devel] Default cache mode, Anthony Liguori, 2011/06/29
Re: [Qemu-devel] Default cache mode, Alexander Graf, 2011/06/29
Re: [Qemu-devel] Default cache mode, Stefan Hajnoczi, 2011/06/29
Re: [Qemu-devel] Default cache mode, Avi Kivity, 2011/06/29