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Re: [Qemu-devel] Default cache mode
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 14:57:17 +0100 |
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.
Your point makes sense though. The default (no explicit cache=)
should mean "the most appropriate caching mode".
Stefan
- 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 <=
Re: [Qemu-devel] Default cache mode, Stefan Hajnoczi, 2011/06/29
Re: [Qemu-devel] Default cache mode, Avi Kivity, 2011/06/29