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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , Alexandre Torgue Cc: Jose Abreu , EricChan , Simon Horman , zhangpengfei16@xiaomi.com, netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH net] net: stmmac: xgmac: do not treat TBU as a TX event Date: Tue, 13 Oct 2026 10:47:47 +0800 Message-ID: <20261013024747.2688984-1-zhangfeionline@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit 8d07a7930434 ("net: stmmac: xgmac: Do not enable TBU interrupt") removed TBUE from the default DMA interrupt mask, but did not remove the TBU check from dwxgmac2_dma_interrupt(). TBU is set whenever a TX channel runs out of descriptors. Since TBUE is not enabled and only enabled bits are cleared, the TBU status bit is never cleared. As a result, TBU stays set on every idle TX channel, regardless of whether there is any TX traffic. With a shared interrupt, stmmac_dma_interrupt() checks all channels, so every interrupt from any source schedules TX NAPI on every idle TX channel. Only use TI to trigger TX processing. Fixes: 8d07a7930434 ("net: stmmac: xgmac: Do not enable TBU interrupt") Signed-off-by: Pengfei Zhang --- Tested on a board with 8 RX/TX DMA channels behind one shared interrupt. A peer sends 10k UDP packets/s to the board and the board sends nothing back, so there should be almost no TX work. Every idle channel reads DMA_CH_STATUS 0x4 (TBU only). Per second, averaged over 10 s: before after hw interrupts 9071 8580 tx_normal_irq_n 72572 1 tx_clean ~73000 9 - hw interrupts: the shared interrupt line, from /proc/interrupts. Unchanged, the RX watchdog sets the rate. - tx_normal_irq_n (ethtool -S): how often dwxgmac2_dma_interrupt() returned handle_tx. Before the fix every interrupt reports it for all 8 channels. - tx_clean (ethtool -S): stmmac_tx_clean() runs, i.e. TX NAPI polls. Each spurious handle_tx schedules one. What is left after the fix is real TX and the TX coalesce timer. The "before" value is from a separate run with the same setup. No packet loss before or after. drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c index ff83858ebc..0a6e82a155 100644 --- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c +++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c @@ -346,7 +346,7 @@ static int dwxgmac2_dma_interrupt(struct stmmac_priv *priv, u64_stats_update_end(&stats->syncp); ret |= handle_rx; } - if (likely(intr_status & (XGMAC_TI | XGMAC_TBU))) { + if (likely(intr_status & XGMAC_TI)) { u64_stats_update_begin(&stats->syncp); u64_stats_inc(&stats->tx_normal_irq_n[chan]); u64_stats_update_end(&stats->syncp); -- 2.54.0