Messages in this thread | | | Date | Thu, 3 Aug 2023 14:55:37 +0200 | Subject | Re: [PATCH V3 net-next] net: fec: add XDP_TX feature support | From | Jesper Dangaard Brouer <> |
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On 03/08/2023 13.18, Wei Fang wrote: >> On 03/08/2023 05.58, Wei Fang wrote: >>>>> } else { >>>>> - xdp_return_frame(xdpf); >>>>> + xdp_return_frame_rx_napi(xdpf); >>>> If you implement Jesper's syncing suggestions, I think you can use >>>> >>>> page_pool_put_page(pool, page, 0, true); >> To Jakub, using 0 here you are trying to bypass the DMA-sync (which is valid >> as driver knows XDP_TX have already done the sync). >> The code will still call into DMA-sync calls with zero as size, so wonder if we >> should detect size zero and skip that call? >> (I mean is this something page_pool should support.) >> [...] >> >> >>>> for XDP_TX here to avoid the DMA sync on page recycle. >>> I tried Jasper's syncing suggestion and used page_pool_put_page() to >>> recycle pages, but the results does not seem to improve the >>> performance of XDP_TX, >> The optimization will only have effect on those devices which have >> dev->dma_coherent=false else DMA function [1] (e.g. >> dma_direct_sync_single_for_device) will skip the sync calls. >> >> [1] https://elixir.bootlin.com/linux/v6.5-rc4/source/kernel/dma/direct.h#L63 >> >> (Cc. Andrew Lunn) >> Does any of the imx generations have dma-noncoherent memory? >> >> And does any of these use the fec NIC driver? >> >>> it even degrades the speed. >> >> Could be low runs simply be a variation between your test runs? >> > Maybe, I just tested once before. So I test several times again, the > results of the two methods do not seem to be much different so far, > both about 255000 pkt/s. > >> The specific device (imx8mpevk) this was tested on, clearly have >> dma_coherent=true, or else we would have seen a difference. >> But the code change should not have any overhead for the >> dma_coherent=true case, the only extra overhead is the extra empty DMA >> sync call with size zero (as discussed in top). >> > The FEC of i.MX8MP-EVK has dma_coherent=false, and as I mentioned > above, I did not see an obvious difference in the performance. :(
That is surprising - given the results.
(see below, lack of perf/diff might be caused by Ethernet flow-control).
> >>> The result of the current modification. >>> root@imx8mpevk:~# ./xdp2 eth0 >>> proto 17: 260180 pkt/s >> >> These results are*significantly* better than reported in patch-1. >> What happened?!? >> > The test environment is slightly different, in patch-1, the FEC port was > directly connected to the port of another board. But in the latest test, > the ports of the two boards were connected to a switch, so the ports of > the two boards are not directly connected. >
Hmm, I've seen this kind of perf behavior of direct-connected or via switch before. The mistake I made was, that I had not disabled Ethernet flow-control. The xdp2 XDP_TX program will swap the mac addresses, and send the packet back to the packet generator (running pktgen), which will get overloaded itself and starts sending Ethernet flow-control pause frames.
Command line to disable: # ethtool -A eth0 rx off tx off
Can I ask/get you to make sure that Ethernet flow-control is disabled (on both generator and DUT (to be on safe-side)) and run the test again?
--Jesper
>> e.g. >> root@imx8mpevk:~# ./xdp2 eth0 >> proto 17: 135817 pkt/s >> proto 17: 142776 pkt/s >> >>> proto 17: 260373 pkt/s >>> proto 17: 260363 pkt/s >>> proto 17: 259036 pkt/s [...] >>> >>> After using the sync suggestion, the result shows as follow. >>> root@imx8mpevk:~# ./xdp2 eth0 >>> proto 17: 255956 pkt/s >>> proto 17: 255841 pkt/s >>> proto 17: 255835 pkt/s
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