From 5323d3e50c20ce53b9b393ef36b027d6cd1e6f11 Mon Sep 17 00:00:00 2001 From: Filip Bakreski Date: Tue, 9 Jun 2026 20:53:01 +1000 Subject: [PATCH] wifi: mt76: mt76u: use a threaded NAPI for the RX path The USB RX path delivers frames to the stack via mt76_rx_complete() with a NULL napi pointer, taking the netif_receive_skb_list() path, so it never benefits from GRO -- unlike the DMA-based mt76 drivers, which pass a real napi and use napi_gro_receive(). For bulk TCP traffic this is costly, as every segment traverses the stack individually. Service the MT_RXQ_MAIN queue from a threaded NAPI, reusing mt76_dev's existing napi_dev and napi[] rather than adding new fields. The URB completion handler schedules the napi; its poll drains the URBs, builds the skbs, resubmits and delivers them through napi_gro_receive(). The MCU queue stays on the existing RX worker. This enables GRO and moves RX processing into its own kernel thread, parallelising the datapath. On mt7921u at HE-MCS 11 (2x2, 80 MHz; fast.com, multiple streams) this averages ~588 Mbit/s, versus ~424 Mbit/s when the same napi is instead driven manually from the RX worker, and ~380 Mbit/s for the unmodified driver. Suggested-by: Lorenzo Bianconi Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Filip Bakreski Acked-by: Lorenzo Bianconi Link: https://patch.msgid.link/20260609105301.196302-1-phial@phiality.com Signed-off-by: Felix Fietkau --- drivers/net/wireless/mediatek/mt76/usb.c | 64 +++++++++++++++++++++--- 1 file changed, 57 insertions(+), 7 deletions(-) diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c index d9638a9b749b..e54b35e53b6a 100644 --- a/drivers/net/wireless/mediatek/mt76/usb.c +++ b/drivers/net/wireless/mediatek/mt76/usb.c @@ -580,7 +580,11 @@ static void mt76u_complete_rx(struct urb *urb) q->head = (q->head + 1) % q->ndesc; q->queued++; - mt76_worker_schedule(&dev->usb.rx_worker); + + if (q == &dev->q_rx[MT_RXQ_MAIN]) + napi_schedule(&dev->napi[MT_RXQ_MAIN]); + else + mt76_worker_schedule(&dev->usb.rx_worker); out: spin_unlock_irqrestore(&q->lock, flags); } @@ -618,11 +622,23 @@ mt76u_process_rx_queue(struct mt76_dev *dev, struct mt76_queue *q) } mt76u_submit_rx_buf(dev, qid, urb); } - if (qid == MT_RXQ_MAIN) { - local_bh_disable(); - mt76_rx_poll_complete(dev, MT_RXQ_MAIN, NULL); - local_bh_enable(); - } +} + +/* Threaded NAPI poll for the MAIN RX queue: drain URBs, build skbs, resubmit, + * then deliver through napi_gro_receive() and let napi_complete() flush GRO. + */ +static int mt76u_napi_poll(struct napi_struct *napi, int budget) +{ + struct mt76_dev *dev = mt76_priv(napi->dev); + + rcu_read_lock(); + mt76u_process_rx_queue(dev, &dev->q_rx[MT_RXQ_MAIN]); + mt76_rx_poll_complete(dev, MT_RXQ_MAIN, napi); + rcu_read_unlock(); + + napi_complete(napi); + + return 0; } static void mt76u_rx_worker(struct mt76_worker *w) @@ -632,8 +648,13 @@ static void mt76u_rx_worker(struct mt76_worker *w) int i; rcu_read_lock(); - mt76_for_each_q_rx(dev, i) + mt76_for_each_q_rx(dev, i) { + /* MT_RXQ_MAIN is serviced by the threaded NAPI poll */ + if (i == MT_RXQ_MAIN) + continue; + mt76u_process_rx_queue(dev, &dev->q_rx[i]); + } rcu_read_unlock(); } @@ -731,6 +752,13 @@ void mt76u_stop_rx(struct mt76_dev *dev) for (j = 0; j < q->ndesc; j++) usb_poison_urb(q->entry[j].urb); } + + /* The MAIN queue napi stays enabled for the device lifetime. The URBs + * are now poisoned, so mt76u_complete_rx() can no longer reschedule it; + * just drain any in-flight poll before the caller frees or resets. + */ + if (dev->napi_dev) + napi_synchronize(&dev->napi[MT_RXQ_MAIN]); } EXPORT_SYMBOL_GPL(mt76u_stop_rx); @@ -1051,6 +1079,13 @@ void mt76u_queues_deinit(struct mt76_dev *dev) mt76u_stop_rx(dev); mt76u_stop_tx(dev); + if (dev->napi_dev) { + napi_disable(&dev->napi[MT_RXQ_MAIN]); + netif_napi_del(&dev->napi[MT_RXQ_MAIN]); + free_netdev(dev->napi_dev); + dev->napi_dev = NULL; + } + mt76u_free_rx(dev); mt76u_free_tx(dev); } @@ -1078,6 +1113,7 @@ int __mt76u_init(struct mt76_dev *dev, struct usb_interface *intf, { struct usb_device *udev = interface_to_usbdev(intf); struct mt76_usb *usb = &dev->usb; + struct mt76_dev **priv; int err; INIT_WORK(&usb->stat_work, mt76u_tx_status_data); @@ -1115,6 +1151,20 @@ int __mt76u_init(struct mt76_dev *dev, struct usb_interface *intf, sched_set_fifo_low(usb->rx_worker.task); sched_set_fifo_low(usb->status_worker.task); + /* threaded NAPI on a dummy netdev (reusing mt76_dev's napi_dev/napi[]) + * services the MAIN RX queue and gives the RX path GRO + */ + dev->napi_dev = alloc_netdev_dummy(sizeof(struct mt76_dev *)); + if (!dev->napi_dev) + return -ENOMEM; + + priv = netdev_priv(dev->napi_dev); + *priv = dev; + strscpy(dev->napi_dev->name, "mt76u-rx", sizeof(dev->napi_dev->name)); + dev->napi_dev->threaded = 1; + netif_napi_add(dev->napi_dev, &dev->napi[MT_RXQ_MAIN], mt76u_napi_poll); + napi_enable(&dev->napi[MT_RXQ_MAIN]); + return 0; } EXPORT_SYMBOL_GPL(__mt76u_init);