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

From: Paolo Bonzini <pbonzini@redhat.com>
To: unlisted-recipients:; (no To-header on input)
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com,
	anthony@codemonkey.ws, kwolf@redhat.com, rusty@rustcorp.com.au
Subject: Re: [QEMU PATCH 0/2] virtio-blk: writeback cache enable improvements
Date: Mon, 23 Jul 2012 18:32:38 +0200	[thread overview]
Message-ID: <500D7CA6.5090901@redhat.com> (raw)
In-Reply-To: <1341321642-24598-1-git-send-email-pbonzini@redhat.com>

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?

Paolo