linux-kernel - Re: BTRFS: Unbelievably slow with kvm/qemu

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Date:	Mon, 12 Jul 2010 15:15:31 +0200
From:	Giangiacomo Mariotti <gg.mariotti@...il.com>
To:	"Justin P. Mattock" <justinmattock@...il.com>
Cc:	Michael Tokarev <mjt@....msk.ru>, linux-kernel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: BTRFS: Unbelievably slow with kvm/qemu

On Mon, Jul 12, 2010 at 9:17 AM, Justin P. Mattock
<justinmattock@...il.com> wrote:
> On 07/12/2010 12:09 AM, Michael Tokarev wrote:
>>
>> This looks quite similar to a problem with ext4 and O_SYNC which I
>> reported earlier but no one cared to answer (or read?) - there:
>> http://permalink.gmane.org/gmane.linux.file-systems/42758
>> (sent to qemu-devel and linux-fsdevel lists - Cc'd too).  You can
>> try a few other options, esp. cache=none and re-writing some guest
>> files to verify.
>>
>> /mjt
>
> cool a solution... glad to see... no chance at a bisect with this?
> (getting this down too a commit or two makes things easier)
>
> Justin P. Mattock
>
I didn't even say what kernel version I was using, sorry! Kernel
2.6.34.1+"patches in stable queue for next stable release". I tried
this some time ago with 2.6.33.x(don't remember which version exactly)
and it had the same problem, but at the time I stopped trying thinking
that it was a kvm problem. So basically there's no known(to me) good
version and no, I can't bisect this because this is my production
system. Anyway, I suspect this is reproducible. Am I the only one who
created a virtual hd file on a Btrfs and then used it with kvm/qemu? I
mean, it's not a particularly exotic test-case!


-- 
Giangiacomo
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