Re: [PATCH 3/3] igb: Get rid of spurious interrupts

[Joe Damato <jdamato@fastly.com>]

On Mon, Feb 10, 2025 at 10:19:37AM +0100, Kurt Kanzenbach wrote:
> When running the igc with XDP/ZC in busy polling mode with deferral of hard
> interrupts, interrupts still happen from time to time. That is caused by
> the igc task watchdog which triggers Rx interrupts periodically.
> 
> That mechanism has been introduced to overcome skb/memory allocation
> failures [1]. So the Rx clean functions stop processing the Rx ring in case
> of such failure. The task watchdog triggers Rx interrupts periodically in
> the hope that memory became available in the mean time.
> 
> The current behavior is undesirable for real time applications, because the
> driver induced Rx interrupts trigger also the softirq processing. However,
> all real time packets should be processed by the application which uses the
> busy polling method.
> 
> Therefore, only trigger the Rx interrupts in case of real allocation
> failures. Introduce a new flag for signaling that condition.
> 
> Follow the same logic as in commit 8dcf2c212078 ("igc: Get rid of spurious
> interrupts").
> 
> [1] - https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=3be507547e6177e5c808544bd6a2efa2c7f1d436
> 
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> ---
>  drivers/net/ethernet/intel/igb/igb.h      |  3 ++-
>  drivers/net/ethernet/intel/igb/igb_main.c | 29 +++++++++++++++++++++++++----
>  drivers/net/ethernet/intel/igb/igb_xsk.c  |  1 +
>  3 files changed, 28 insertions(+), 5 deletions(-)

I am not an igb expert (nor do I have such a device), but after
reading the source a bit this seems reasonable.

I suppose perhaps a better direction in the future would be to
convert the driver to the page pool, but in the meantime the
proposed change seems reasonable.

Reviewed-by: Joe Damato <jdamato@fastly.com>