On Wed, 28 Apr 2021 09:41:52 +0200 Magnus Karlsson <magnus.karlsson@xxxxxxxxx> wrote: > On Tue, Apr 27, 2021 at 8:28 PM Lorenzo Bianconi <lorenzo@xxxxxxxxxx> wrote: > > > > [...] > > > > > Took your patches for a test run with the AF_XDP sample xdpsock on an > > > i40e card and the throughput degradation is between 2 to 6% depending > > > on the setup and microbenchmark within xdpsock that is executed. And > > > this is without sending any multi frame packets. Just single frame > > > ones. Tirtha made changes to the i40e driver to support this new > > > interface so that is being included in the measurements. > > > > > > What performance do you see with the mvneta card? How much are we > > > willing to pay for this feature when it is not being used or can we in > > > some way selectively turn it on only when needed? > > > > Hi Magnus, > > > > Today I carried out some comparison tests between bpf-next and bpf-next + > > xdp_multibuff series on mvneta running xdp_rxq_info sample. Results are > > basically aligned: > > > > bpf-next: > > - xdp drop ~ 665Kpps > > - xdp_tx ~ 291Kpps > > - xdp_pass ~ 118Kpps > > > > bpf-next + xdp_multibuff: > > - xdp drop ~ 672Kpps > > - xdp_tx ~ 288Kpps > > - xdp_pass ~ 118Kpps > > > > I am not sure if results are affected by the low power CPU, I will run some > > tests on ixgbe card. > > Thanks Lorenzo. I made some new runs, this time with i40e driver > changes as a new data point. Same baseline as before but with patches > [1] and [2] applied. Note > that if you use net or net-next and i40e, you need patch [3] too. > > The i40e multi-buffer support will be posted on the mailing list as a > separate RFC patch so you can reproduce and review. > > Note, calculations are performed on non-truncated numbers. So 2 ns > might be 5 cycles on my 2.1 GHz machine since 2.49 ns * 2.1 GHz = > 5.229 cycles ~ 5 cycles. xdpsock is run in zero-copy mode so it uses > the zero-copy driver data path in contrast with xdp_rxq_info that uses > the regular driver data path. Only ran the busy-poll 1-core case this > time. Reported numbers are the average over 3 runs. Yes, for i40e the xdpsock zero-copy test uses another code path, this is something we need to keep in mind. Also remember that we designed the central xdp_do_redirect() call to delay creation of xdp_frame. This is something what AF_XDP ZC takes advantage of. Thus, the cost of xdp_buff to xdp_frame conversion is not covered in below tests, and I expect this patchset to increase that cost... (UPDATE: below XDP_TX actually does xdp_frame conversion) > multi-buffer patches without any driver changes: Thanks you *SO* much Magnus for these superb tests. I absolutely love how comprehensive your test results are. Thanks you for catching the performance regression in this patchset. (I for one know how time consuming these kind of tests are, I appreciate your effort, a lot!) > xdpsock rxdrop 1-core: > i40e: -4.5% in throughput / +3 ns / +6 cycles > ice: -1.5% / +1 ns / +2 cycles > > xdp_rxq_info -a XDP_DROP > i40e: -2.5% / +2 ns / +3 cycles > ice: +6% / -3 ns / -7 cycles > > xdp_rxq_info -a XDP_TX > i40e: -10% / +15 ns / +32 cycles > ice: -9% / +14 ns / +29 cycles This is a clear performance regression. Looking closer at driver i40e_xmit_xdp_tx_ring() actually performs a xdp_frame conversion calling xdp_convert_buff_to_frame(xdp). FYI: We have started an offlist thread on finding the root-cause and on IRC with Lorenzo. The current lead is that, as Alexei so wisely pointed out in earlier patches, that struct bit access is not efficient... As I expect we soon need bits for HW RX checksum indication, and indication if metadata contains BTF described area, I've asked Lorenzo to consider this, and look into introducing a flags member. (Then we just have to figure out how to make flags access efficient). > multi-buffer patches + i40e driver changes from Tirtha: > > xdpsock rxdrop 1-core: > i40e: -3% / +2 ns / +3 cycles > > xdp_rxq_info -a XDP_DROP > i40e: -7.5% / +5 ns / +9 cycles > > xdp_rxq_info -a XDP_TX > i40e: -10% / +15 ns / +32 cycles > > Would be great if someone could rerun a similar set of experiments on > i40e or ice then > report. > [1] https://lists.osuosl.org/pipermail/intel-wired-lan/Week-of-Mon-20210419/024106.html > [2] https://lists.osuosl.org/pipermail/intel-wired-lan/Week-of-Mon-20210426/024135.html > [3] https://lists.osuosl.org/pipermail/intel-wired-lan/Week-of-Mon-20210426/024129.html I'm very happy that you/we all are paying attention to keep XDP performance intact, as small 'paper-cuts' like +32 cycles does affect XDP in the long run. Happy performance testing everybody :-) -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
