Zvi Effron wrote: > On Tue, May 4, 2021 at 4:07 PM Zvi Effron <zeffron@xxxxxxxxxxxxx> wrote: > > I'm suspecting it's something with how XDP_REDIRECT is implemented in > > the i40e driver, but I don't know if this is a) cross driver behavior, > > b) expected behavior, or c) a bug. > I think I've found the issue, and it appears to be specific to i40e > (and maybe other drivers, too, but not XDP itself). > > When performing the XDP xmit, i40e uses the smp_processor_id() to > select the tx queue (see > https://elixir.bootlin.com/linux/v5.12.1/source/drivers/net/ethernet/intel/i40e/i40e_txrx.c#L3846). > I'm not 100% clear on how the CPU is selected (since we don't use > cores 0 and 1), we end up on a core whose id is higher than any > available queue. > > I'm going to try to modify our IRQ mappings to test this. > > If I'm correct, this feels like a bug to me, since it requires a user > to understand low level driver details to do IRQ remapping, which is a > bit higher level. But if it's intended, we'll just have to figure out > how to work around this. (Unfortunately, using split tx and rx queues > is not possible with i40e, so that easy solution is unavailable.) > > --Zvi It seems like for Intel drivers, igc, ixgbe, i40e, ice all have this problem. Notably, igb, fixes it like I would expect. Let's talk about it over on intel-wired-lan and cc netdev. Jesse
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