netdev - Re: [PATCH iwl-next v2] igc: Get rid of spurious interrupts

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Message-ID: <3f8aef95-e7f8-4c47-9b19-a2ba90c4a532@amd.com>
Date: Tue, 23 Jul 2024 08:53:29 -0700
From: Brett Creeley <bcreeley@....com>
To: Kurt Kanzenbach <kurt@...utronix.de>,
 Jesse Brandeburg <jesse.brandeburg@...el.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
 Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [PATCH iwl-next v2] igc: Get rid of spurious interrupts



On 6/20/2024 11:56 PM, Kurt Kanzenbach wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
> 
> 
> 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.
> 
> [1] - https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=3be507547e6177e5c808544bd6a2efa2c7f1d436
> 
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Acked-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
> ---
> Changes in v2:
> - Index Rx rings correctly
> - Link to v1: https://lore.kernel.org/r/20240611-igc_irq-v1-1-49763284cb57@linutronix.de
> ---
>   drivers/net/ethernet/intel/igc/igc.h      |  1 +
>   drivers/net/ethernet/intel/igc/igc_main.c | 30 ++++++++++++++++++++++++++----
>   2 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
> index 8b14c029eda1..7bfe5030e2c0 100644
> --- a/drivers/net/ethernet/intel/igc/igc.h
> +++ b/drivers/net/ethernet/intel/igc/igc.h
> @@ -682,6 +682,7 @@ enum igc_ring_flags_t {
>          IGC_RING_FLAG_TX_DETECT_HANG,
>          IGC_RING_FLAG_AF_XDP_ZC,
>          IGC_RING_FLAG_TX_HWTSTAMP,
> +       IGC_RING_FLAG_RX_ALLOC_FAILED,
>   };
> 
>   #define ring_uses_large_buffer(ring) \
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index 87b655b839c1..850ef6b8b202 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c

<snip>

> @@ -5811,11 +5815,29 @@ static void igc_watchdog_task(struct work_struct *work)
>          if (adapter->flags & IGC_FLAG_HAS_MSIX) {
>                  u32 eics = 0;
> 
> -               for (i = 0; i < adapter->num_q_vectors; i++)
> -                       eics |= adapter->q_vector[i]->eims_value;
> -               wr32(IGC_EICS, eics);
> +               for (i = 0; i < adapter->num_q_vectors; i++) {
> +                       struct igc_q_vector *q_vector = adapter->q_vector[i];
> +                       struct igc_ring *rx_ring;
> +
> +                       if (!q_vector->rx.ring)
> +                               continue;
> +
> +                       rx_ring = adapter->rx_ring[q_vector->rx.ring->queue_index];
> +
> +                       if (test_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags)) {
> +                               eics |= q_vector->eims_value;
> +                               clear_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
> +                       }

Tiny nit, but is there a reason to not use test_and_clear_bit() here?

> +               }
> +               if (eics)
> +                       wr32(IGC_EICS, eics);
>          } else {
> -               wr32(IGC_ICS, IGC_ICS_RXDMT0);
> +               struct igc_ring *rx_ring = adapter->rx_ring[0];
> +
> +               if (test_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags)) {
> +                       clear_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
> +                       wr32(IGC_ICS, IGC_ICS_RXDMT0);
> +               }

Also here?

Thanks,

Brett

>          }
> 
>          igc_ptp_tx_hang(adapter);
> 
> ---
> base-commit: a6ec08beec9ea93f342d6daeac922208709694dc
> change-id: 20240611-igc_irq-ccc1c8bc6890
> 
> Best regards,
> --
> Kurt Kanzenbach <kurt@...utronix.de>
> 
>