[Qemu-devel] Re: [PATCH +stable] block: don't attempt to merge overlapping requests

[Avi Kivity]

On 05/19/2010 12:01 PM, Stefan Hajnoczi wrote:
> On Wed, May 19, 2010 at 9:09 AM, Avi Kivity<address@hidden>  wrote:
>    
> > On 05/18/2010 10:22 PM, Stefan Hajnoczi wrote:
> >      
> > > What cache= mode are you running?
> > >        
> > writeback.
> >      
> In the cache=writeback case the virtio-blk guest driver does:
>
> blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH, ...)
>    

I don't follow.  What's the implication?

btw I really dislike how the cache attribute (which I see as a pure host 
choice) is exposed to the guest.  It means we can't change caching mode 
on the fly (for example after live migration), or that changing caching 
mode during a restart may expose a previously hidden guest bug.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.