* [PATCH] wifi: mt76: mt76u: use GRO on the USB RX path
@ 2026-06-08 4:41 Filip Bakreski
2026-06-08 17:40 ` Lorenzo Bianconi
0 siblings, 1 reply; 3+ messages in thread
From: Filip Bakreski @ 2026-06-08 4:41 UTC (permalink / raw)
To: nbd, lorenzo, ryder.lee; +Cc: shayne.chen, sean.wang, linux-wireless
The USB RX path delivers frames to the stack via mt76_rx_complete() with
a NULL napi pointer, which takes the netif_receive_skb_list() path and
therefore never benefits from GRO. The DMA-based mt76 drivers pass a real
napi and get napi_gro_receive(); the USB path does not. For bulk TCP
traffic this is costly, as every segment traverses the network stack
individually instead of being coalesced.
Add a small container NAPI on a dummy netdev that the RX worker drives
manually: napi_schedule_prep() marks it scheduled, frames are delivered
through napi_gro_receive(), and napi_complete_done() flushes the coalesced
list. The poll handler is never invoked by the core.
On mt7921u at HE-MCS 11 (2x2, 80 MHz) this raises single-stream TCP
download throughput from ~383 to ~475 Mbit/s (~+24%), averaged over six
interleaved A/B measurements. The gain only applies while the link is not
RF-limited, as expected for a host-side optimisation.
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Filip Bakreski <phial@phiality.com>
---
drivers/net/wireless/mediatek/mt76/mt76.h | 4 +++
drivers/net/wireless/mediatek/mt76/usb.c | 36 ++++++++++++++++++++++-
2 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
index 07955555f..f5e52c1f4 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76.h
+++ b/drivers/net/wireless/mediatek/mt76/mt76.h
@@ -668,6 +668,10 @@ struct mt76_usb {
struct mt76_worker status_worker;
struct mt76_worker rx_worker;
+ /* container NAPI used only to batch GRO for the RX worker */
+ struct net_device *napi_dev;
+ struct napi_struct napi;
+
struct work_struct stat_work;
u8 out_ep[__MT_EP_OUT_MAX];
diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index d9638a9b7..f9c48140c 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -619,12 +619,31 @@ mt76u_process_rx_queue(struct mt76_dev *dev, struct mt76_queue *q)
mt76u_submit_rx_buf(dev, qid, urb);
}
if (qid == MT_RXQ_MAIN) {
+ struct napi_struct *napi = &dev->usb.napi;
+
local_bh_disable();
- mt76_rx_poll_complete(dev, MT_RXQ_MAIN, NULL);
+ /* Drive a container NAPI so the RX path can use
+ * napi_gro_receive(): napi_schedule_prep() marks it SCHED and
+ * napi_complete_done() flushes the coalesced GRO list. The poll
+ * handler is never actually invoked by the core.
+ */
+ if (dev->usb.napi_dev && napi_schedule_prep(napi)) {
+ mt76_rx_poll_complete(dev, MT_RXQ_MAIN, napi);
+ napi_complete_done(napi, 1);
+ } else {
+ mt76_rx_poll_complete(dev, MT_RXQ_MAIN, NULL);
+ }
local_bh_enable();
}
}
+/* Never invoked by the core: the RX worker drives GRO via the napi manually. */
+static int mt76u_napi_poll(struct napi_struct *napi, int budget)
+{
+ napi_complete(napi);
+ return 0;
+}
+
static void mt76u_rx_worker(struct mt76_worker *w)
{
struct mt76_usb *usb = container_of(w, struct mt76_usb, rx_worker);
@@ -1051,6 +1070,13 @@ void mt76u_queues_deinit(struct mt76_dev *dev)
mt76u_stop_rx(dev);
mt76u_stop_tx(dev);
+ if (dev->usb.napi_dev) {
+ napi_disable(&dev->usb.napi);
+ netif_napi_del(&dev->usb.napi);
+ free_netdev(dev->usb.napi_dev);
+ dev->usb.napi_dev = NULL;
+ }
+
mt76u_free_rx(dev);
mt76u_free_tx(dev);
}
@@ -1115,6 +1141,14 @@ 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);
+ /* container netdev + NAPI used only to enable GRO on the RX path */
+ usb->napi_dev = alloc_netdev_dummy(0);
+ if (!usb->napi_dev)
+ return -ENOMEM;
+ strscpy(usb->napi_dev->name, "mt76u-rx", sizeof(usb->napi_dev->name));
+ netif_napi_add(usb->napi_dev, &usb->napi, mt76u_napi_poll);
+ napi_enable(&usb->napi);
+
return 0;
}
EXPORT_SYMBOL_GPL(__mt76u_init);
base-commit: 5f6099446d1ddb888e36cdf93b6a0551f05c1267
--
2.54.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] wifi: mt76: mt76u: use GRO on the USB RX path
2026-06-08 4:41 [PATCH] wifi: mt76: mt76u: use GRO on the USB RX path Filip Bakreski
@ 2026-06-08 17:40 ` Lorenzo Bianconi
2026-06-09 0:35 ` Filip Bakreski
0 siblings, 1 reply; 3+ messages in thread
From: Lorenzo Bianconi @ 2026-06-08 17:40 UTC (permalink / raw)
To: Filip Bakreski; +Cc: nbd, ryder.lee, shayne.chen, sean.wang, linux-wireless
[-- Attachment #1: Type: text/plain, Size: 4557 bytes --]
> The USB RX path delivers frames to the stack via mt76_rx_complete() with
> a NULL napi pointer, which takes the netif_receive_skb_list() path and
> therefore never benefits from GRO. The DMA-based mt76 drivers pass a real
> napi and get napi_gro_receive(); the USB path does not. For bulk TCP
> traffic this is costly, as every segment traverses the network stack
> individually instead of being coalesced.
>
> Add a small container NAPI on a dummy netdev that the RX worker drives
> manually: napi_schedule_prep() marks it scheduled, frames are delivered
> through napi_gro_receive(), and napi_complete_done() flushes the coalesced
> list. The poll handler is never invoked by the core.
>
> On mt7921u at HE-MCS 11 (2x2, 80 MHz) this raises single-stream TCP
> download throughput from ~383 to ~475 Mbit/s (~+24%), averaged over six
> interleaved A/B measurements. The gain only applies while the link is not
> RF-limited, as expected for a host-side optimisation.
>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Filip Bakreski <phial@phiality.com>
> ---
> drivers/net/wireless/mediatek/mt76/mt76.h | 4 +++
> drivers/net/wireless/mediatek/mt76/usb.c | 36 ++++++++++++++++++++++-
> 2 files changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 07955555f..f5e52c1f4 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -668,6 +668,10 @@ struct mt76_usb {
> struct mt76_worker status_worker;
> struct mt76_worker rx_worker;
>
> + /* container NAPI used only to batch GRO for the RX worker */
> + struct net_device *napi_dev;
> + struct napi_struct napi;
I guess we do not need to add them, we can just reuse napi_dev pointer and
napi[] array available in mt76_dev struct. Agree?
> +
> struct work_struct stat_work;
>
> u8 out_ep[__MT_EP_OUT_MAX];
> diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> index d9638a9b7..f9c48140c 100644
> --- a/drivers/net/wireless/mediatek/mt76/usb.c
> +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> @@ -619,12 +619,31 @@ mt76u_process_rx_queue(struct mt76_dev *dev, struct mt76_queue *q)
> mt76u_submit_rx_buf(dev, qid, urb);
> }
> if (qid == MT_RXQ_MAIN) {
> + struct napi_struct *napi = &dev->usb.napi;
> +
> local_bh_disable();
> - mt76_rx_poll_complete(dev, MT_RXQ_MAIN, NULL);
> + /* Drive a container NAPI so the RX path can use
> + * napi_gro_receive(): napi_schedule_prep() marks it SCHED and
> + * napi_complete_done() flushes the coalesced GRO list. The poll
> + * handler is never actually invoked by the core.
> + */
> + if (dev->usb.napi_dev && napi_schedule_prep(napi)) {
> + mt76_rx_poll_complete(dev, MT_RXQ_MAIN, napi);
> + napi_complete_done(napi, 1);
> + } else {
> + mt76_rx_poll_complete(dev, MT_RXQ_MAIN, NULL);
> + }
> local_bh_enable();
> }
> }
>
> +/* Never invoked by the core: the RX worker drives GRO via the napi manually. */
> +static int mt76u_napi_poll(struct napi_struct *napi, int budget)
> +{
> + napi_complete(napi);
> + return 0;
> +}
> +
> static void mt76u_rx_worker(struct mt76_worker *w)
> {
> struct mt76_usb *usb = container_of(w, struct mt76_usb, rx_worker);
> @@ -1051,6 +1070,13 @@ void mt76u_queues_deinit(struct mt76_dev *dev)
> mt76u_stop_rx(dev);
> mt76u_stop_tx(dev);
>
> + if (dev->usb.napi_dev) {
> + napi_disable(&dev->usb.napi);
> + netif_napi_del(&dev->usb.napi);
> + free_netdev(dev->usb.napi_dev);
> + dev->usb.napi_dev = NULL;
> + }
> +
> mt76u_free_rx(dev);
> mt76u_free_tx(dev);
> }
> @@ -1115,6 +1141,14 @@ 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);
>
> + /* container netdev + NAPI used only to enable GRO on the RX path */
> + usb->napi_dev = alloc_netdev_dummy(0);
> + if (!usb->napi_dev)
> + return -ENOMEM;
> + strscpy(usb->napi_dev->name, "mt76u-rx", sizeof(usb->napi_dev->name));
> + netif_napi_add(usb->napi_dev, &usb->napi, mt76u_napi_poll);
I guess it would be interesting verifying if threaded-napi provides better
results.
Regards,
Lorenzo
> + napi_enable(&usb->napi);
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(__mt76u_init);
>
> base-commit: 5f6099446d1ddb888e36cdf93b6a0551f05c1267
> --
> 2.54.0
>
>
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2026-06-08 4:41 [PATCH] wifi: mt76: mt76u: use GRO on the USB RX path Filip Bakreski
2026-06-08 17:40 ` Lorenzo Bianconi
2026-06-09 0:35 ` Filip Bakreski
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