On Mon, 13 Nov 2017 22:07:47 +0900 Björn Töpel <bjorn.to...@gmail.com> wrote:
> I'll summarize the major points, that we'll address in the next RFC > below. > > * Instead of extending AF_PACKET with yet another version, introduce a > new address/packet family. As for naming had some name suggestions: > AF_CAPTURE, AF_CHANNEL, AF_XDP and AF_ZEROCOPY. We'll go for > AF_ZEROCOPY, unless there're no strong opinions against it. I mostly like AF_CHANNEL and AF_XDP. I do know XDP is/have-evolved-into a kernel-side facility, that moves XDP-frames/packets _inside_ the kernel. *BUT* I've always imagined, that we would create a "channel" to userspace. By using XDP_REDIRECT to choose what frames get redirected into which userspace "channel" (new channel-map type). Userspace pre-allocate and register memory/pages exactly like this patchset. [Step-1]: (non-ZC) XDP_REDIRECT need to copy frame-data into userspace memory pages. And update your packet_array etc. (Use map-flush to get RX bulking). [Step 2]: (ZC) Userspace call driver NDO to register pages. The XDP_REDIRECT action happens in driver, and can have knowledge about RX-ring. It can know if this RX-ring is Zero-Copy enabled and can skip the copy-step. > * No explicit zerocopy enablement. Use the zeropcopy path if > supported, if not -- fallback to the skb path, for netdevs that > don't support the required ndos. When driver does not support NDO in above model. I think, that there will still be a significant performance boost for the non-ZC variant. Even-though we need a copy-operation, because there are no memory allocations. As userspace have preallocated and registered pages with the kernel (and mem-limits are implicit via mem-size reg by userspace). > * Do not introduce a new XDP action XDP_PASS_TO_KERNEL, instead use > XDP redirect map call with ingress flag. In above model, XDP_REDIRECT is used for filtering into a userspace "channel". If ZC gets enabled on a RX-ring queue, then XDP_PASS have to do a copy (RX-ring knowledge is avail), like you describe with XDP_PASS_TO_KERNEL. > * Extend the XDP redirect to support explicit allocator/destructor > functions. Right now, XDP redirect assumes that the page allocator > was used, and the XDP redirect cleanup path is decreasing the page > count of the XDP buffer. This assumption breaks for the zerocopy > case. Yes, please. If XDP_REDIRECT get call a destructor call-back, then we can allow XDP_REDIRECT out another net_device, even-when ZC is enabled on a RX-ring queue. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
