From: Kevin Wolf <kwolf@redhat.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] KVM call agenda for October 25
Date: Wed, 26 Oct 2011 10:15:52 +0200 [thread overview]
Message-ID: <4EA7C1B8.9000903@redhat.com> (raw)
In-Reply-To: <4EA6C25C.8000502@codemonkey.ws>
Am 25.10.2011 16:06, schrieb Anthony Liguori:
> On 10/25/2011 08:56 AM, Kevin Wolf wrote:
>> Am 25.10.2011 15:05, schrieb Anthony Liguori:
>>> I'd be much more open to changing the default mode to cache=none FWIW since the
>>> risk of data loss there is much, much lower.
>>
>> I think people said that they'd rather not have cache=none as default
>> because O_DIRECT doesn't work everywhere.
>
> Where doesn't it work these days? I know it doesn't work on tmpfs. I know it
> works on ext[234], btrfs, nfs.
Besides file systems (and probably OSes) that don't support O_DIRECT,
there's another case: Our defaults don't work on 4k sector disks today.
You need to explicitly specify the logical_block_size qdev property for
cache=none to work on them.
And changing this default isn't trivial as the right value doesn't only
depend on the host disk, but it's also guest visible. The only way out
would be bounce buffers, but I'm not sure that doing that silently is a
good idea...
Kevin
next prev parent reply other threads:[~2011-10-26 8:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-24 11:04 [Qemu-devel] KVM call agenda for October 25 Juan Quintela
2011-10-24 11:35 ` Paolo Bonzini
2011-10-24 12:02 ` Peter Maydell
2011-10-24 13:06 ` Andreas Färber
2011-10-24 15:34 ` Luiz Capitulino
2011-10-25 12:35 ` Kevin Wolf
2011-10-25 13:05 ` Anthony Liguori
2011-10-25 13:18 ` Dor Laor
2011-10-25 13:28 ` Anthony Liguori
2011-10-25 13:40 ` Andreas Färber
2011-10-25 13:56 ` Kevin Wolf
2011-10-25 14:06 ` Anthony Liguori
2011-10-25 15:32 ` Kevin Wolf
2011-10-25 22:19 ` Alexander Graf
2011-10-26 20:41 ` Anthony Liguori
2011-10-26 8:15 ` Kevin Wolf [this message]
2011-10-26 8:48 ` Markus Armbruster
2011-10-26 9:41 ` Paolo Bonzini
2011-10-26 11:12 ` Markus Armbruster
2011-10-26 9:57 ` Daniel P. Berrange
2011-10-26 11:23 ` Kevin Wolf
2011-10-26 11:39 ` Daniel P. Berrange
2011-10-26 12:18 ` Kevin Wolf
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