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Re: [Qemu-devel] Default cache mode
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] Default cache mode |
Date: |
Wed, 29 Jun 2011 14:32:34 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 |
Am 29.06.2011 14:23, schrieb Anthony Liguori:
> On 06/29/2011 07:16 AM, Kevin Wolf wrote:
>> Am 29.06.2011 14:06, schrieb Anthony Liguori:
>>> On 06/29/2011 06:59 AM, Kevin Wolf wrote:
>>>> Hi,
>>>>
>>>> I think we have touched this topic before during some IRC discussions or
>>>> somewhere deep in a mailing list thread, but I think it hasn't been
>>>> discussed on the list.
>>>>
>>>> Our default cache mode of cache=writethrough is extremely conservative
>>>> and provides absolute safety at the cost of performance,
>>>
>>> But for the most part, we track bare metal fairly well in terms of block
>>> performance, no?
>>>
>>> Or are you really referring to qcow2 as a specific example? In the
>>> past, we used a different default caching mode for qcow2. I think that
>>> could be done again if there was a compelling reason.
>>
>> 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.
> At any rate, I'm a big fan of making wce tunable in the guest and then I
> think setting wce=1 is quite reasonable to do by default.
Okay, I think that's a fair requirement. So let's plan to implement this
in 0.16.
Christoph, it looks like we're back to your WCE patches then. Do you
still work on them?
Kevin
- [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 <=
- 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, 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