On Wed, Dec 07, 2016 at 09:14:48PM -0800, John Fastabend wrote: > On 16-12-07 08:48 PM, Michael S. Tsirkin wrote: > > On Wed, Dec 07, 2016 at 12:11:57PM -0800, John Fastabend wrote: > >> From: John Fastabend <john.fastab...@gmail.com> > >> > >> This adds XDP support to virtio_net. Some requirements must be > >> met for XDP to be enabled depending on the mode. First it will > >> only be supported with LRO disabled so that data is not pushed > >> across multiple buffers. Second the MTU must be less than a page > >> size to avoid having to handle XDP across multiple pages. > >> > >> If mergeable receive is enabled this patch only supports the case > >> where header and data are in the same buf which we can check when > >> a packet is received by looking at num_buf. If the num_buf is > >> greater than 1 and a XDP program is loaded the packet is dropped > >> and a warning is thrown. When any_header_sg is set this does not > >> happen and both header and data is put in a single buffer as expected > >> so we check this when XDP programs are loaded. Subsequent patches > >> will process the packet in a degraded mode to ensure connectivity > >> and correctness is not lost even if backend pushes packets into > >> multiple buffers. > >> > >> If big packets mode is enabled and MTU/LRO conditions above are > >> met then XDP is allowed. > >> > >> This patch was tested with qemu with vhost=on and vhost=off where > >> mergeable and big_packet modes were forced via hard coding feature > >> negotiation. Multiple buffers per packet was forced via a small > >> test patch to vhost.c in the vhost=on qemu mode. > >> > >> Suggested-by: Shrijeet Mukherjee <shrij...@gmail.com> > >> Signed-off-by: John Fastabend <john.r.fastab...@intel.com> > > > > I'd like to note that I don't think disabling LRO is a good > > plan long-term. It's really important for virtio performance, > > so IMHO we need a fix for that. > > I'm guessing that a subset of XDP programs would be quite > > happy with just looking at headers, and that is there in the 1st buffer. > > So how about teaching XDP that there could be a truncated packet? > > > > Then we won't have to disable LRO. > > > > Agreed long-term we can drop this requirement this type of improvement > would also allow working with jumbo frames on nics. > > I don't think it should block this patch series though. > > .John
Right.
