From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kevin Wolf <kwolf@redhat.com>
Subject: Re: [PATCH 2/2] virtio-blk: disable write cache if not negotiated
Date: Tue, 03 Jul 2012 15:49:48 +0200
Message-ID: <4FF2F87C.6010600@redhat.com>
References: <1341321642-24598-1-git-send-email-pbonzini@redhat.com> <1341321642-24598-3-git-send-email-pbonzini@redhat.com>
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Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com,
	anthony@codemonkey.ws, rusty@rustcorp.com.au
To: Paolo Bonzini <pbonzini@redhat.com>
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Am 03.07.2012 15:20, schrieb Paolo Bonzini:
> If the guest does not support flushes, we should run in writethrough mode.
> The setting is temporary until the next reset, so that for example the
> BIOS will run in writethrough mode while Linux will run with a writeback
> cache.
> 
> 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 have
> two bugs, 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.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

I generally like the idea for a default, but doesn't this override even
an explicit cache=writeback? Are we sure that we want this?

Kevin