Hello everybody,sorry for bringing this up again, but I didn't receive any answer and I'm still experiencing this problem on kernel 5.14. Does anybody have some insight on whether this is an expected behavior, a bug, or maybe just some problem in my code?
Best regards, Federico Parola On 04/08/21 10:55, Federico Parola wrote:
Dear all,I made some changes to the xdpsock kernel example to support the l2fwd scenario between two interfaces. I didn't use the xsk_fwd sample because I didn't need the complex umem management used there.The updated code can be found here: https://pastebin.com/p54T5nfW(I'd be happy to submit it to the kernel, with proper modifications, if you deem it useful, just let me know).I get a strange behavior when using busy polling on two interfaces. Here are the numbers I get when testing on a Intel XL710 dual port NIC (i40e driver). I ran all the tests on a single core (both user space and interrupts) and tuned the input rate to achieve maximum throughput (this was fundamental in the non busy poll tests). When running in busy poll both interfaces are configured with:$ echo 2 | sudo tee /sys/class/net/<if>/napi_defer_hard_irqs $ echo 200000 | sudo tee /sys/class/net/<if>/gro_flush_timeout TEST | Mpps ---------+------- 1 if | 10.77 1 if BP | 13.01 2 ifs | 9.49 2 ifs BP | 7.25 (BP = busy poll with default batch size, 64)As you can see when I move from 1 interface to 2 interfaces in the non-busy-poll mode performance reduces a bit, but I think this makes sense since we are handling data structures for two ports instead of one (does it make sense?). What I don't understand is why performance on 2 ifs is lower when using busy polling. I made some tests and saw that with two interfaces there is some sofirq CPU usage and the tx port keeps generating interrupts, while this doesn't happen when using a single interface.My question is: should interrupts and softirq processing be disabled on the tx path as well, when using busy polling? Or is it just a rx feature?Best regards, Federico Parola
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