Subject: Re: [Question] Generic way to retrieve IRQ number of Tx/Rx queue

From: Jakub Kicinski <[email-masked]>
Date: Mon, 13 Jan 2025 13:15:08 -0800

On Fri, 10 Jan 2025 10:07:18 +0100 Daniel Sedlak wrote:
> Hello,
> I am writing an affinity scheduler in the userspace for network cards's 
> Tx/Rx queues. Is there a generic way to retrieve all IRQ numbers for 
> those queues for each interface?
> 
> My goal is to get all Tx/Rx queues for a given interface, get the IRQ 
> number of the individual queues, and set an affinity hint for each 
> queue. I have tried to loop over /proc/interrupts to retrieve all queues 
> for an interface in a hope that the last column would contain the 
> interface name however this does not work since the naming is not 
> unified across drivers. My second attempt was to retrieve all registered 
> interrupts by network interface from 
> /sys/class/net/{interface_name}/device/msi_irqs/, but this attempt was 
> also without luck because some drivers request more IRQs than the number 
> of queues (for example i40e driver).

We do have an API for that
https://docs.kernel.org/next/networking/netlink_spec/netdev.html#napi
but unfortunately the driver needs to support it, and i40e currently
doesn't:

$ git grep --files-with-matches  netif_napi_set_irq 
drivers/net/ethernet/amazon/ena/ena_netdev.c
drivers/net/ethernet/broadcom/bnxt/bnxt.c
drivers/net/ethernet/broadcom/tg3.c
drivers/net/ethernet/google/gve/gve_utils.c
drivers/net/ethernet/intel/e1000/e1000_main.c
drivers/net/ethernet/intel/e1000e/netdev.c
drivers/net/ethernet/intel/ice/ice_lib.c
drivers/net/ethernet/intel/igc/igc_main.c
drivers/net/ethernet/mellanox/mlx4/en_cq.c
drivers/net/ethernet/mellanox/mlx5/core/en_main.c
drivers/net/ethernet/meta/fbnic/fbnic_txrx.c

Should be easy to add. Let me CC the Intel list in case they already
have a relevant change queued for i40e..