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Re: [Qemu-devel] Default cache mode
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 16:50:08 +0200 |
User-agent: |
Mutt/1.5.17 (2007-11-01) |
On Wed, Jun 29, 2011 at 06:17:02PM +0400, Michael Tokarev wrote:
> > Honestly, I don't know. Usually the problem is resolved with setting a
> > different cache option, so nobody bothers to ask for details. I'd guess
> > that it's ext4 in most cases.
>
> Extremly poor performance also happens on raw devices --
> be it lvm volumes or plain partitions, so that's w/o
> any filesystem.
Depends on your setup. If you have ATA devices that have WCE=1
it will suck due to the non-queueable FLUSH command. If you have
an older kernel with the draining barriers semantics it will to.
If you run on a SAS disk or FC array with WCE=0 performance will
be quite good and close to native performance on these.
That's all assuming you use O_DIRECT. using cache=writhrough
as-is will suck everywher.
- [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Anthony Liguori, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Anthony Liguori, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Michael Tokarev, 2011/06/29
- Re: [Qemu-devel] Default cache mode,
Christoph Hellwig <=
- Re: [Qemu-devel] Default cache mode, Michael Tokarev, 2011/06/29
- 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, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Stefan Hajnoczi, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Frediano Ziglio, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29
- Re: [Qemu-devel] Default cache mode, Kevin Wolf, 2011/06/29
Re: [Qemu-devel] Default cache mode, Christoph Hellwig, 2011/06/29