From: Fil Dunsky mt76 enables threaded NAPI for the dma rx queues, but the napi kthreads stay SCHED_OTHER, unlike the usb and sdio rx/status workers and the tx worker, which already use sched_set_fifo_low(). On MT7621 (MIPS 1004Kc, 2 cores / 4 threads, PREEMPT_NONE, HZ=100) with MT7612E (mt76x2e) as a 5 GHz client receiving ~200 Mbit/s while userspace keeps the CPUs busy, the napi kthread is regularly delayed by 10-30 ms or more and the 256-entry rx ring fills up completely (instrumented: ~500 full-ring events in 5 minutes). Occasionally the chip's rx DMA does not resume after such an event: WPDMA_GLO_CFG reports rx and tx DMA busy, RXQ_STA shows the PBF rx queue at RX_MAX_PCNT, the host ring has free buffers, beacons are lost, then tx DMA stops (dma_idx stuck with frames queued), the tx hang watchdog fires, followed by "MCU message ... timed out" and a second restart. A series of these sometimes hangs the whole system. With the napi kthreads at SCHED_FIFO 1 the ring overflowed once in 5 minutes, no watchdog resets occurred in repeated 5 minute runs and rx throughput in the same setup went from ~210 to ~280 Mbit/s. A larger rx ring (1024 entries) did not help: it still overflowed and resets were more frequent. Set the napi kthread priority right after netif_napi_add(), as done for the other workers. Signed-off-by: Fil Dunsky --- Tested on Securifi Almond 3 (MT7621, MT7612E + MT7602E) with OpenWrt 25.12.6 (kernel 6.12.112, mt76 2026-03-19 39c960c3 plus this change): iperf3 bidirectional, 4 streams, 5 GHz client link at -66 dBm, with a userspace proxy and a display daemon running. Without the change 2-3 watchdog resets in most 5 minute runs and several full-system hangs; with it 0 resets over 6 runs. A similar reset chain under full CPU load on MT7620A + MT7612E is reported in https://github.com/openwrt/openwrt/issues/8984 --- drivers/net/wireless/mediatek/mt76/dma.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/wireless/mediatek/mt76/dma.c b/drivers/net/wireless/mediatek/mt76/dma.c index a67880a92..8e66fad7b 100644 --- a/drivers/net/wireless/mediatek/mt76/dma.c +++ b/drivers/net/wireless/mediatek/mt76/dma.c @@ -1128,6 +1128,11 @@ mt76_dma_rx_queue_init(struct mt76_dev *dev, enum mt76_rxq_id qid, int (*poll)(struct napi_struct *napi, int budget)) { netif_napi_add(dev->napi_dev, &dev->napi[qid], poll); + /* Same as the usb/sdio rx workers: under CPU load a SCHED_OTHER napi + * thread can be starved long enough for the rx ring to overflow. + */ + if (dev->napi[qid].thread) + sched_set_fifo_low(dev->napi[qid].thread); mt76_dma_rx_fill_buf(dev, &dev->q_rx[qid], false); napi_enable(&dev->napi[qid]); } --- base-commit: 6474fa070f2b8013b4b87350b775b8c3be6e8aac change-id: 20261020-b4-mt76-napi-fifo-dc5ef4fc24b4 Best regards, -- Fil Dunsky