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
