On 07/11/2017 11:01 AM, Jesper Dangaard Brouer wrote: > On Tue, 11 Jul 2017 10:48:29 -0700 > John Fastabend <john.fastab...@gmail.com> wrote: > >> On 07/11/2017 08:36 AM, Jesper Dangaard Brouer wrote: >>> On Sat, 8 Jul 2017 21:06:17 +0200 >>> Jesper Dangaard Brouer <bro...@redhat.com> wrote: >>> >>>> My plan is to test this latest patchset again, Monday and Tuesday. >>>> I'll try to assess stability and provide some performance numbers. >>> >>> Performance numbers: >>> >>> 14378479 pkt/s = XDP_DROP without touching memory >>> 9222401 pkt/s = xdp1: XDP_DROP with reading packet data >>> 6344472 pkt/s = xdp2: XDP_TX with swap mac (writes into pkt) >>> 4595574 pkt/s = xdp_redirect: XDP_REDIRECT with swap mac (simulate >>> XDP_TX) >>> 5066243 pkt/s = xdp_redirect_map: XDP_REDIRECT with swap mac + devmap >>> >>> The performance drop between xdp2 and xdp_redirect, was expected due >>> to the HW-tailptr flush per packet, which is costly. >>> >>> (1/6344472-1/4595574)*10^9 = -59.98 ns >>> >>> The performance drop between xdp2 and xdp_redirect_map, is higher than >>> I expected, which is not good! The avoidance of the tailptr flush per >>> packet was expected to give a higher boost. The cost increased with >>> 40 ns, which is too high compared to the code added (on a 4GHz machine >>> approx 160 cycles). >>> >>> (1/6344472-1/5066243)*10^9 = -39.77 ns >>> >>> This system doesn't have DDIO, thus we are stalling on cache-misses, >>> but I was actually expecting that the added code could "hide" behind >>> these cache-misses. >>> >>> I'm somewhat surprised to see this large a performance drop. >>> >> >> Yep, although there is room for optimizations in the code path for sure. And >> 5mpps is not horrible my preference is to get this series in plus any >> small optimization we come up with while the merge window is closed. Then >> follow up patches can do optimizations. > > IMHO 5Mpps is a very bad number for XDP. > >> One easy optimization is to get rid of the atomic bitops. They are not needed >> here we have a per cpu unsigned long. Another easy one would be to move >> some of the checks out of the hotpath. For example checking for ndo_xdp_xmit >> and flush ops on the net device in the hotpath really should be done in the >> slow path. > > I'm already running with a similar patch as below, but it > (surprisingly) only gave my 3 ns improvement. I also tried a > prefetchw() on xdp.data that gave me 10 ns (which is quite good). >
Ah OK good, do the above numbers use the both the bitops changes and the prefechw? > I'm booting up another system with a CPU E5-1650 v4 @ 3.60GHz, which > have DDIO ... I have high hopes for this, as the major bottleneck on > this CPU i7-4790K CPU @ 4.00GHz is clearly cache-misses. > > Something is definitely wrong on this CPU, as perf stats shows, a very > bad utilization of the CPU pipeline with 0.89 insn per cycle. > Interesting, the E5-1650 numbers will be good to know. If you have the perf trace to posting might help track down some hot spots. .John
