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Re: [Qemu-devel] Default cache mode
From: |
Michael Tokarev |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 18:17:02 +0400 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.1.16) Gecko/20110506 Icedove/3.0.11 |
29.06.2011 16:32, Kevin Wolf wrote:
> Am 29.06.2011 14:23, schrieb Anthony Liguori:
>> On 06/29/2011 07:16 AM, Kevin Wolf wrote:
>>> No, people are also complaining about bad performance with raw. Which
>>> isn't really surprising when you do a flush after each single write
>>> request. O_SYNC is really much more than is needed in the average case.
>>
>> Which file system on the host?
>
> 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. Sure, a filesystem adds quite noticeable
overhead (because of mtime updates and that sort of things),
but _just_ syncronous writes are enough to kill performance.
/mjt
- [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 <=
- 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, 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