Re: [PATCH] vhost-net: utilize PUBLISH_USED_IDX feature

[Avi Kivity]

On 05/20/2010 01:27 AM, Michael S. Tsirkin wrote:
> On Wed, May 19, 2010 at 08:04:51PM +0300, Avi Kivity wrote:
>    
> > On 05/18/2010 04:19 AM, Michael S. Tsirkin wrote:
> >      
> > > With PUBLISH_USED_IDX, guest tells us which used entries
> > > it has consumed. This can be used to reduce the number
> > > of interrupts: after we write a used entry, if the guest has not yet
> > > consumed the previous entry, or if the guest has already consumed the
> > > new entry, we do not need to interrupt.
> > > This imporves bandwidth by 30% under some workflows.
> > >
> > > Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx>
> > > ---
> > >
> > > Rusty, Dave, this patch depends on the patch
> > > "virtio: put last seen used index into ring itself"
> > > which is currently destined at Rusty's tree.
> > > Rusty, if you are taking that one for 2.6.35, please
> > > take this one as well.
> > > Dave, any objections?
> > >
> > >        
> > I object: I think the index should have its own cacheline,
> >      
> The issue here is that host/guest do not know each
> other's cache line size. I guess we could just put it
> at offset 128 or something like that ... Rusty?
>    

Not so pretty, but ok.

>    
> > and that it should be documented before merging.
> >      
> I think you meant to object to the virtio patch, not this one.  This
> patch does not introduce new layout, just implements host support.
> virtio spec patch will follow: it is not part of linux tree so
> there is no patch dependency.
>    

There is a reviewer dependency.

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

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