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

From: Avi Kivity
Date: Wed May 19 2010 - 13:05:46 EST

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, and that it should be documented before merging.

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

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