Toke Høiland-Jørgensen <toke@xxxxxxxxxx> 于2023年8月8日周二 20:01写道： > > Albert Huang <huangjie.albert@xxxxxxxxxxxxx> writes: > > > AF_XDP is a kernel bypass technology that can greatly improve performance. > > However,for virtual devices like veth,even with the use of AF_XDP sockets, > > there are still many additional software paths that consume CPU resources. > > This patch series focuses on optimizing the performance of AF_XDP sockets > > for veth virtual devices. Patches 1 to 4 mainly involve preparatory work. > > Patch 5 introduces tx queue and tx napi for packet transmission, while > > patch 8 primarily implements batch sending for IPv4 UDP packets, and patch 9 > > add support for AF_XDP tx need_wakup feature. These optimizations significantly > > reduce the software path and support checksum offload. > > > > I tested those feature with > > A typical topology is shown below: > > client(send): server:(recv) > > veth<-->veth-peer veth1-peer<--->veth1 > > 1 | | 7 > > |2 6| > > | | > > bridge<------->eth0(mlnx5)- switch -eth1(mlnx5)<--->bridge1 > > 3 4 5 > > (machine1) (machine2) > > I definitely applaud the effort to improve the performance of af_xdp > over veth, this is something we have flagged as in need of improvement > as well. > > However, looking through your patch series, I am less sure that the > approach you're taking here is the right one. > > AFAIU (speaking about the TX side here), the main difference between > AF_XDP ZC and the regular transmit mode is that in the regular TX mode > the stack will allocate an skb to hold the frame and push that down the > stack. Whereas in ZC mode, there's a driver NDO that gets called > directly, bypassing the skb allocation entirely. > > In this series, you're implementing the ZC mode for veth, but the driver > code ends up allocating an skb anyway. Which seems to be a bit of a > weird midpoint between the two modes, and adds a lot of complexity to > the driver that (at least conceptually) is mostly just a > reimplementation of what the stack does in non-ZC mode (allocate an skb > and push it through the stack). > > So my question is, why not optimise the non-zc path in the stack instead > of implementing the zc logic for veth? It seems to me that it would be > quite feasible to apply the same optimisations (bulking, and even GRO) > to that path and achieve the same benefits, without having to add all > this complexity to the veth driver? > > -Toke > thanks! This idea is really good indeed. You've reminded me, and that's something I overlooked. I will now consider implementing the solution you've proposed and test the performance enhancement. Albert.
