Re: [Qemu-devel] [PATCH 2/2] virtio-blk: disable write cache if not negotiated

[Kevin Wolf]

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 <address@hidden>

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