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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo