From: Michael Tokarev <mjt@tls.msk.ru>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
Avi Kivity <avi@redhat.com>, Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] Default cache mode
Date: Wed, 29 Jun 2011 18:17:02 +0400 [thread overview]
Message-ID: <4E0B33DE.5000706@msgid.tls.msk.ru> (raw)
In-Reply-To: <4E0B1B62.9080309@redhat.com>
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
next prev parent reply other threads:[~2011-06-29 14:17 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-29 11:59 [Qemu-devel] Default cache mode Kevin Wolf
2011-06-29 12:06 ` Anthony Liguori
2011-06-29 12:16 ` Kevin Wolf
2011-06-29 12:23 ` Anthony Liguori
2011-06-29 12:32 ` Kevin Wolf
2011-06-29 13:51 ` Christoph Hellwig
2011-06-29 14:17 ` Michael Tokarev [this message]
2011-06-29 14:50 ` Christoph Hellwig
2011-06-29 15:07 ` Michael Tokarev
2011-06-29 13:50 ` Christoph Hellwig
2011-06-29 14:13 ` Anthony Liguori
2011-06-29 14:47 ` Christoph Hellwig
2011-06-29 16:03 ` Stefan Hajnoczi
2011-06-29 13:53 ` Frediano Ziglio
2011-06-29 14:11 ` Kevin Wolf
2011-06-29 14:12 ` Christoph Hellwig
2011-06-29 14:21 ` Kevin Wolf
2011-06-29 13:49 ` Christoph Hellwig
2011-06-29 12:08 ` Anthony Liguori
2011-06-29 13:55 ` Christoph Hellwig
2011-06-29 14:20 ` Anthony Liguori
2011-06-29 14:52 ` Christoph Hellwig
2011-06-29 15:26 ` Anthony Liguori
2011-06-29 12:21 ` Alexander Graf
2011-06-29 13:57 ` Stefan Hajnoczi
2011-06-29 14:05 ` Alexander Graf
2011-06-29 12:52 ` Stefan Hajnoczi
2011-06-29 13:56 ` Christoph Hellwig
2011-06-29 13:00 ` Avi Kivity
2011-06-29 13:05 ` Anthony Liguori
2011-06-29 13:30 ` Avi Kivity
2011-06-29 13:11 ` Kevin Wolf
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