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Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive |
Date: |
Wed, 26 May 2010 16:12:39 +0200 |
User-agent: |
Mozilla-Thunderbird 2.0.0.22 (X11/20090707) |
Anthony Liguori a écrit :
> On 05/26/2010 03:52 AM, Aurelien Jarno wrote:
>> On Tue, May 25, 2010 at 08:31:20PM -0500, Anthony Liguori wrote:
>>
>>> On 05/25/2010 04:01 PM, Aurelien Jarno wrote:
>>>
>>>> I really think this patch can be useful, in my own case when testing
>>>> debian-installer (I already cache=writeback). In short all that is about
>>>> developing and testing, as opposed to run a VM in production, can
>>>> benefit about that. This was one of the original use case of QEMU before
>>>> KVM arrived.
>>>>
>>>> Unless someone can convince me not to do it, I seriously considering
>>>> applying this patch.
>>>>
>>> There really needs to be an indication in the --help output of what
>>> the ramifications of this option are, in the very least. It should
>>>
>> That's indeed something than can be done, but to avoid double standards,
>> it should also be done for other features that can lead to data
>> corruption. I am talking for example on the qcow format, which is not
>> really supported anymore.
>>
>
> I agree.
>
>>> also be removable via a ./configure option because no sane
>>> distribution should enable this for end users.
>>>
>>>
>> I totally disagree. All the examples I have given apply to qemu *users*,
>> not qemu developers. They surely don't want to recompile qemu for their
>> usage. Note also that what is proposed in this patch was the default not
>> too long ago, and that a lot of users complained about the new default
>> for their usage, they see it as a regression. We even had to put a note
>> explaining that in the Debian package to avoid to many bug reports.
>> cache=writeback only answer partially to this use case.
>>
>
> It's hard for me to consider this a performance regression because
> ultimately, you're getting greater than bare metal performance (because
> of extremely aggressive caching). It might be a regression from the
> previous performance, but that was at the cost of safety.
For people who don't care about safety it's still a regression. And it
is a common usage of QEMU.
> We might get 100 bug reports about this "regression" but they concern
> much less than 1 bug report of image corruption because of power
> failure/host crash. A reputation of being unsafe is very difficult to
> get rid of and is something that I hear concerns about frequently.
>
> I'm not suggesting that the compile option should be disabled by default
> upstream. But the option should be there for distributions because I
> hope that any enterprise distro disables it.
>
Which basically means those distro don't care about some use cases of
QEMU, that were for most of them the original uses cases. It's sad.
Sometimes I really whishes that KVM never tried to reintegrate code into
QEMU, it doesn't bring only good things.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, (continued)
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Kevin Wolf, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Kevin Wolf, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Kevin Wolf, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Aurelien Jarno, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Aurelien Jarno, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Kevin Wolf, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/26
- [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Paolo Bonzini, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive,
Aurelien Jarno <=
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Aurelien Jarno, 2010/05/26
- Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/26
Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Avi Kivity, 2010/05/26
[Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive, Anthony Liguori, 2010/05/17