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

From: Avi Kivity <[email-masked]>
Date: Wed, 19 May 2010 20:04:51 +0300

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<[email-masked]>
> ---
>
> 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, and that it 
should be documented before merging.

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