MANA hardware requires at least one doorbell ring every 8 wraparounds of the CQ. The driver rings the doorbell as a form of flow control to inform hardware that CQEs have been consumed.
The NAPI poll functions mana_poll_tx_cq() and mana_poll_rx_cq() can poll up to CQE_POLLING_BUFFER (512) completions per call. If the CQ has fewer than 512 entries, a single poll call can process more than 4 wraparounds without ringing the doorbell. The doorbell threshold check also uses ">" instead of ">=", delaying the ring by one extra CQE beyond 4 wraparounds. Combined, these issues can cause the driver to exceed the 8-wraparound hardware limit, leading to missed completions and stalled queues. Fix this by capping the number of CQEs polled per call to 4 wraparounds of the CQ in both TX and RX paths. Also change the doorbell threshold from ">" to ">=" so the doorbell is rung as soon as 4 wraparounds are reached. Cc: [email protected] Fixes: 58a63729c957 ("net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings") Signed-off-by: Long Li <[email protected]> --- drivers/net/ethernet/microsoft/mana/mana_en.c | 23 +++++++++++++++---- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c index 9919183ad39e..fe667e0d930d 100644 --- a/drivers/net/ethernet/microsoft/mana/mana_en.c +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c @@ -1770,8 +1770,14 @@ static void mana_poll_tx_cq(struct mana_cq *cq) ndev = txq->ndev; apc = netdev_priv(ndev); + /* Limit CQEs polled to 4 wraparounds of the CQ to ensure the + * doorbell can be rung in time for the hardware's requirement + * of at least one doorbell ring every 8 wraparounds. + */ comp_read = mana_gd_poll_cq(cq->gdma_cq, completions, - CQE_POLLING_BUFFER); + min_t(u32, (cq->gdma_cq->queue_size / + COMP_ENTRY_SIZE) * 4, + CQE_POLLING_BUFFER)); if (comp_read < 1) return; @@ -2156,7 +2162,14 @@ static void mana_poll_rx_cq(struct mana_cq *cq) struct mana_rxq *rxq = cq->rxq; int comp_read, i; - comp_read = mana_gd_poll_cq(cq->gdma_cq, comp, CQE_POLLING_BUFFER); + /* Limit CQEs polled to 4 wraparounds of the CQ to ensure the + * doorbell can be rung in time for the hardware's requirement + * of at least one doorbell ring every 8 wraparounds. + */ + comp_read = mana_gd_poll_cq(cq->gdma_cq, comp, + min_t(u32, (cq->gdma_cq->queue_size / + COMP_ENTRY_SIZE) * 4, + CQE_POLLING_BUFFER)); WARN_ON_ONCE(comp_read > CQE_POLLING_BUFFER); rxq->xdp_flush = false; @@ -2201,11 +2214,11 @@ static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue) mana_gd_ring_cq(gdma_queue, SET_ARM_BIT); cq->work_done_since_doorbell = 0; napi_complete_done(&cq->napi, w); - } else if (cq->work_done_since_doorbell > - cq->gdma_cq->queue_size / COMP_ENTRY_SIZE * 4) { + } else if (cq->work_done_since_doorbell >= + (cq->gdma_cq->queue_size / COMP_ENTRY_SIZE) * 4) { /* MANA hardware requires at least one doorbell ring every 8 * wraparounds of CQ even if there is no need to arm the CQ. - * This driver rings the doorbell as soon as we have exceeded + * This driver rings the doorbell as soon as it has processed * 4 wraparounds. */ mana_gd_ring_cq(gdma_queue, 0); -- 2.43.0
