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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Dragos Tatulea , Mina Almasry , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Bobby Eshleman Subject: Re: [PATCH net v3] net/mlx5e: fix BQL reset on SQ re-activation Message-ID: References: <20260803-mlx5-bql-v3-1-a30d4c66fe1d@meta.com> <6ac643bf-c6f4-4ff2-ba57-964a645d9323@nvidia.com> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6ac643bf-c6f4-4ff2-ba57-964a645d9323@nvidia.com> On Tue, Aug 04, 2026 at 11:23:53AM +0300, Tariq Toukan wrote: > > > On 04/08/2026 2:47, Bobby Eshleman wrote: > > From: Bobby Eshleman > > > > mlx5e_queue_start() deactivates and re-activates all channels but closes > > only the queue being restarted. mlx5e_activate_txqsq() then > > unconditionally calls netdev_tx_reset_queue(), zeroing the BQL counters > > of channels that kept their in-flight TX WQEs. The next completion then > > over-charges and trips the BUG_ON() in dql_completed(): > > > > kernel BUG at lib/dynamic_queue_limits.c:99! > > RIP: 0010:dql_completed+0x23d/0x280 > > Call Trace: > > > > mlx5e_poll_tx_cq+0x668/0xa60 > > mlx5e_napi_poll+0x5b/0x7b0 > > net_rx_action+0x15a/0x580 > > > > Reset BQL only when the SQ has no bytes in flight (sq->cc == sq->pc). > > > > In the case that reset is skipped, the outstanding WQEs will eventually > > complete and rebalance the dql. The dql->limit is carried across the > > reset. > > > > Fixes: b2588ea40ec9 ("net/mlx5e: Implement queue mgmt ops and single channel swap") > > Signed-off-by: Bobby Eshleman > > Reviewed-by: Tariq Toukan > > Thanks. Thanks Tariq, and my apologies for forgetting to carry the R-b forward. > > > --- > > Changes in v3: > > - Sample sq->cc/sq->pc before setting MLX5E_SQ_STATE_ENABLED, so a > > concurrent mlx5e_poll_tx_cq() cannot un-charge BQL between the check > > and netdev_tx_reset_queue() (Sashiko: > > https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260729-mlx5-bql-v2-1-cdf285e586df@meta.com) > > - Link to v2: https://lore.kernel.org/r/20260729-mlx5-bql-v2-1-cdf285e586df@meta.com > > > > Changes in v2: > > - remove misleading comment (Tariq) > > - Link to v1: https://lore.kernel.org/r/20260728-mlx5-bql-v1-1-99a0ab77ede7@meta.com > > --- > > drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > > index 7d47a1da8b6b..f0407a850ea8 100644 > > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > > @@ -1939,8 +1939,10 @@ int mlx5e_open_txqsq(struct mlx5e_channel *c, u32 tisn, int txq_ix, > > void mlx5e_activate_txqsq(struct mlx5e_txqsq *sq) > > { > > sq->txq = netdev_get_tx_queue(sq->netdev, sq->txq_ix); > > + /* Reset BQL only when the SQ has no bytes in flight. */ > > + if (sq->cc == sq->pc) > > + netdev_tx_reset_queue(sq->txq); > > set_bit(MLX5E_SQ_STATE_ENABLED, &sq->state); > > - netdev_tx_reset_queue(sq->txq); > > netif_tx_start_queue(sq->txq); > > netif_queue_set_napi(sq->netdev, sq->txq_ix, NETDEV_QUEUE_TYPE_TX, sq->cq.napi); > > } > > > > --- > > base-commit: d1000fd7995e51deec872d154e0a40d82f7a539f > > change-id: 20260728-mlx5-bql-84e02a5a46c8 > > > > Best regards, >