On Mon, 9 Dec 2019 18:45:12 +0100 Björn Töpel <bjorn.topel@xxxxxxxxx> wrote: > On Mon, 9 Dec 2019 at 18:00, Jesper Dangaard Brouer <brouer@xxxxxxxxxx> wrote: > > > > On Mon, 9 Dec 2019 14:55:16 +0100 > > Björn Töpel <bjorn.topel@xxxxxxxxx> wrote: > > > > > Performance > > > =========== > > > > > > The tests were performed using the xdp_rxq_info sample program with > > > the following command-line: > > > > > > 1. XDP_DRV: > > > # xdp_rxq_info --dev eth0 --action XDP_DROP > > > 2. XDP_SKB: > > > # xdp_rxq_info --dev eth0 -S --action XDP_DROP > > > 3. xdp-perf, from selftests/bpf: > > > # test_progs -v -t xdp_perf > > > > > > > > > Run with mitigations=auto > > > ------------------------- > > > > > > Baseline: > > > 1. 22.0 Mpps > > > 2. 3.8 Mpps > > > 3. 15 ns > > > > > > Dispatcher: > > > 1. 29.4 Mpps (+34%) > > > 2. 4.0 Mpps (+5%) > > > 3. 5 ns (+66%) > > > > Thanks for providing these extra measurement points. This is good > > work. I just want to remind people that when working at these high > > speeds, it is easy to get amazed by a +34% improvement, but we have to > > be careful to understand that this is saving approx 10 ns time or > > cycles. > > > > In reality cycles or time saved in #2 (3.8 Mpps -> 4.0 Mpps) is larger > > (1/3.8-1/4)*1000 = 13.15 ns. Than #1 (22.0 Mpps -> 29.4 Mpps) > > (1/22-1/29.4)*1000 = 11.44 ns. Test #3 keeps us honest 15 ns -> 5 ns = > > 10 ns. The 10 ns improvement is a big deal in XDP context, and also > > correspond to my own experience with retpoline (approx 12 ns overhead). > > > > Ok, good! :-) > > > To Bjørn, I would appreciate more digits on your Mpps numbers, so I get > > more accuracy on my checks-and-balances I described above. I suspect > > the 3.8 Mpps -> 4.0 Mpps will be closer to the other numbers when we > > get more accuracy. > > > > Ok! Let me re-run them. Well, I don't think you should waste your time re-running these... It clearly shows a significant improvement. I'm just complaining that I didn't have enough digits to do accurate checks-and-balances, they are close enough that I believe them. > If you have some spare cycles, yt would be > great if you could try it out as well on your Mellanox setup. I'll add it to my TODO list... but no promises. > Historically you've always been able to get more stable numbers than > I. :-) > > > > > > Dispatcher (full; walk all entries, and fallback): > > > 1. 20.4 Mpps (-7%) > > > 2. 3.8 Mpps > > > 3. 18 ns (-20%) > > > > > > Run with mitigations=off > > > ------------------------ > > > > > > Baseline: > > > 1. 29.6 Mpps > > > 2. 4.1 Mpps > > > 3. 5 ns > > > > > > Dispatcher: > > > 1. 30.7 Mpps (+4%) > > > 2. 4.1 Mpps > > > 3. 5 ns > > > > While +4% sounds good, but could be measurement noise ;-) > > > > (1/29.6-1/30.7)*1000 = 1.21 ns > > > > As both #3 says 5 ns. > > > > True. Maybe that simply hints that we shouldn't use the dispatcher here? No. I actually think it is worth exposing this code as much as possible. And if it really is 1.2 ns improvement, then I'll gladly take that as well ;-) I think this is awesome work! -- thanks for doing this!!! -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
