Messages in this thread | | | Subject | Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice | From | Shirley Ma <> | Date | Wed, 25 May 2011 15:49:40 -0700 |
| |
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
| |