On Fri, 2011-05-20 at 02:41 +0300, Michael S. Tsirkin wrote: > So the requirements are > - data must be released in a timely fashion (e.g. unlike virtio-net > tun or bridge) The current patch doesn't enable tun zero-copy. tun will copy data It's not an issue now. We can disallow macvtap attach to bridge when zero-copy is enabled. > - SG support > - HIGHDMA support (on arches where this makes sense) This can be checked by device flags. > - no filtering based on data (data is mapped in guest) > - on fast path no calls to skb_copy, skb_clone, pskb_copy, > pskb_expand_head as these are slow Any calls to skb_copy, skb_clone, pskb_copy, pskb_expand_head will do a copy. The performance should be the same as none zero-copy case before. I have done/tested the patch V6, will send it out for review tomorrow. I am looking at where there are some cases, skb remains the same for filtering. > First 2 requirements are a must, all other requirements > are just dependencies to make sure zero copy will be faster > than non zero copy. > Using a new feature bit is probably the simplest approach to > this. macvtap on top of most physical NICs most likely works > correctly so it seems a bit more work than it needs to be, > but it's also the safest one I think ... For "macvtap/vhost zero-copy" we can use SG & HIGHDMA to enable it, it looks safe to me once patching skb_copy, skb_clone, pskb_copy, pskb_expand_head. To extend zero-copy in other usages, we can have a new feature bit later. Is that reasonable? Thanks Shirley -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
