From: Kevin Wolf <kwolf@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
Frediano Ziglio <freddy77@gmail.com>, Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] Default cache mode
Date: Wed, 29 Jun 2011 16:21:42 +0200 [thread overview]
Message-ID: <4E0B34F6.8080406@redhat.com> (raw)
In-Reply-To: <20110629141206.GA16311@lst.de>
Am 29.06.2011 16:12, schrieb Christoph Hellwig:
> On Wed, Jun 29, 2011 at 04:11:53PM +0200, Kevin Wolf wrote:
>> If the guest is acting correctly, then this assumption is definitely
>> true with cache=none/writeback. What needs to happen is that the guest
>> issues a disk flush before sending your "transaction ok" message. If it
>> doesn't do that it can fail even on real hardware. cache=writethrough
>> makes things safe that aren't even safe on real hardware, that's why I
>> consider it extremely conservative.
>
> Depends on your defintion of real hardware. Traditionally disks always
> had WCE=0 semantics. When ATA disks added volatile writecaches and people
> started seeing problems due to it the advertisement of cache modes and
> cache flush commands were added. For non-ATA disks like SAS or FC
> WCE=1 still is the typical delivery setting.
Sure, I'm not saying that it definitely breaks on any hardware, just
that it can break.
Kevin
next prev parent reply other threads:[~2011-06-29 14:19 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
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 [this message]
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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