Re: [QEMU PATCH 0/2] virtio-blk: writeback cache enable improvements

From: Kevin Wolf <kwolf@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com,
	anthony@codemonkey.ws, rusty@rustcorp.com.au
Subject: Re: [QEMU PATCH 0/2] virtio-blk: writeback cache enable improvements
Date: Wed, 01 Aug 2012 18:25:05 +0200	[thread overview]
Message-ID: <50195861.2080601@redhat.com> (raw)
In-Reply-To: <501950C0.4050201@redhat.com>

Am 01.08.2012 17:52, schrieb Paolo Bonzini:
> Il 23/07/2012 18:32, Paolo Bonzini ha scritto:
>> Il 03/07/2012 15:20, Paolo Bonzini ha scritto:
>>>> These patches let virtio-blk use the new support for toggling the cache
>>>> mode between writethrough and writeback.
>>>>
>>>> The first patch introduces a new feature bit and configuration field to
>>>> do this.  The second patch disables writeback caching for guests that do
>>>> not negotiate VIRTIO_BLK_F_WCACHE (meaning that they cannot send flush
>>>> requests), so that limited or older guests are now safe wrt power losses.
>>>> VIRTIO_BLK_F_FLUSH has been introduced in Linux 2.6.32 (in 2009) and was
>>>> backported to RHEL/CentOS 5.6 (in 2010).
>>>>
>>>> The Windows drivers (which work by emulating SCSI on top of virtio-blk)
>>>> have bugs in this area, which I reported on the Red Hat Bugzilla as
>>>> bugs 837321 and 837324.  With these patches they will suffer a
>>>> performance hit but gain correctness.
>>>>
>>>> Paolo Bonzini (2):
>>>>   virtio-blk: support VIRTIO_BLK_F_CONFIG_WCE
>>>>   virtio-blk: disable write cache if not negotiated
>> Ping - Anthony, mst?
> 
> Ping^2, so we can switch writethrough->writeback in 1.2.

Speak now or forever hold your peace. If there are no more comments
until Friday, I'll just apply it.

Kevin