> Subject: [EXTERNAL] Re: [PATCH net] net: mana: Ring doorbell at 4 CQ > wraparounds > > On 25/02/2026 18:49, Long Li wrote: > > 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 / > > no need for min_t, simple min() can be used, queue_size is already u32
Thank you, I'm sending v2. Long > > > + 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 / > > same here > > > + COMP_ENTRY_SIZE) * 4, > > + CQE_POLLING_BUFFER)); > > WARN_ON_ONCE(comp_read > CQE_POLLING_BUFFER); > > > > rxq->xdp_flush = false;
