Re: Dropped packets mapping IRQs for adjusted queue counts on i40e

On 5/5/21 12:55 PM, Zvi Effron wrote:
> On Tue, May 4, 2021 at 4:07 PM Zvi Effron <[email protected]> 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.
> 


that is known problem; mlx5 has that constraint too.