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Wed, 21 Oct 2026 07:59:18 -0700 (PDT) Received: from [127.0.1.1] ([85.249.168.112]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5bfa4b90999sm128327e87.68.2026.10.21.07.59.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 07:59:17 -0700 (PDT) From: Fil Dunsky To: nbd@nbd.name, lorenzo@kernel.org, ryder.lee@mediatek.com Cc: shayne.chen@mediatek.com, sean.wang@mediatek.com, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, Fil Dunsky , netdev@vger.kernel.org Subject: Re: [PATCH] wifi: mt76: dma: run threaded NAPI kthreads with SCHED_FIFO low priority In-Reply-To: <20261020-b4-mt76-napi-fifo-v1-1-ac8a24e2062a@gmail.com> References: <20261020-b4-mt76-napi-fifo-v1-1-ac8a24e2062a@gmail.com> Date: Wed, 21 Oct 2026 17:25:53 +0300 Message-ID: <179259275334.35963.15413466304986880275@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Adding netdev to Cc, as suggested on the GitHub mirror of this patch [1], since it touches the scheduling policy of threaded NAPI kthreads. For context on why this is done in the driver rather than left to the admin (chrt / sysfs): mt76 already does exactly this for its other rx/status and tx workers (sched_set_fifo_low() for the usb and sdio workers and for the tx worker), so the dma napi kthreads were the only mt76 rx path left at SCHED_OTHER. A userspace chrt also has to race the creation of the napi threads at boot and module reload. Numbers from the setup in the commit message (MT7621 + MT7612E as 5 GHz client, 3 runs x 5 min each, ~200-280 Mbit/s rx with userspace load): stock: ~500 full-ring events / 5 min, watchdog resets and MCU timeouts, occasional hard hang this patch: 0 resets in 3 runs, rx 276-288 Mbit/s stock + chrt -f 1: 0 resets in 3 runs, rx 249-273 Mbit/s napi_threaded=0: 0 resets rx ring 1024 (stock): 800-1300 full-ring events / run, more resets A similar restart pattern is reported on single-core MT7620 at much lower rates [2], which fits CPU contention rather than throughput as the trigger. [1] https://github.com/openwrt/mt76/pull/1164 [2] https://github.com/openwrt/mt76/issues/457 Thanks, Fil