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[93.34.89.13]) by smtp.googlemail.com with ESMTPSA id q28-20020adfab1c000000b003248a490e3asm2048211wrc.39.2023.10.18.05.35.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 05:35:59 -0700 (PDT) From: Christian Marangi To: Raju Rangoju , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexandre Torgue , Jose Abreu , Maxime Coquelin , Ping-Ke Shih , Kalle Valo , Simon Horman , Daniel Borkmann , Jiri Pirko , Hangbin Liu , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-wireless@vger.kernel.org Cc: Christian Marangi Subject: [net-next PATCH v4 2/4] net: stmmac: improve TX timer arm logic Date: Wed, 18 Oct 2023 14:35:48 +0200 Message-Id: <20231018123550.27110-3-ansuelsmth@gmail.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231018123550.27110-1-ansuelsmth@gmail.com> References: <20231018123550.27110-1-ansuelsmth@gmail.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231018_053603_612206_267824F4 X-CRM114-Status: GOOD ( 21.55 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org There is currently a problem with the TX timer getting armed multiple unnecessary times causing big performance regression on some device that suffer from heavy handling of hrtimer rearm. The use of the TX timer is an old implementation that predates the napi implementation and the interrupt enable/disable handling. Due to stmmac being a very old code, the TX timer was never evaluated again with this new implementation and was kept there causing performance regression. The performance regression started to appear with kernel version 4.19 with 8fce33317023 ("net: stmmac: Rework coalesce timer and fix multi-queue races") where the timer was reduced to 1ms causing it to be armed 40 times more than before. Decreasing the timer made the problem more present and caused the regression in the other of 600-700mbps on some device (regression where this was notice is ipq806x). The problem is in the fact that handling the hrtimer on some target is expensive and recent kernel made the timer armed much more times. A solution that was proposed was reverting the hrtimer change and use mod_timer but such solution would still hide the real problem in the current implementation. To fix the regression, apply some additional logic and skip arming the timer when not needed. Arm the timer ONLY if a napi is not already scheduled. Running the timer is redundant since the same function (stmmac_tx_clean) will run in the napi TX poll. Also try to cancel any timer if a napi is scheduled to prevent redundant run of TX call. With the following new logic the original performance are restored while keeping using the hrtimer. Signed-off-by: Christian Marangi --- .../net/ethernet/stmicro/stmmac/stmmac_main.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index bb1dbf4c9f6c..5124ee87286c 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -2996,13 +2996,25 @@ static void stmmac_tx_timer_arm(struct stmmac_priv *priv, u32 queue) { struct stmmac_tx_queue *tx_q = &priv->dma_conf.tx_queue[queue]; u32 tx_coal_timer = priv->tx_coal_timer[queue]; + struct stmmac_channel *ch; + struct napi_struct *napi; if (!tx_coal_timer) return; - hrtimer_start(&tx_q->txtimer, - STMMAC_COAL_TIMER(tx_coal_timer), - HRTIMER_MODE_REL); + ch = &priv->channel[tx_q->queue_index]; + napi = tx_q->xsk_pool ? &ch->rxtx_napi : &ch->tx_napi; + + /* Arm timer only if napi is not already scheduled. + * Try to cancel any timer if napi is scheduled, timer will be armed + * again in the next scheduled napi. + */ + if (unlikely(!napi_is_scheduled(napi))) + hrtimer_start(&tx_q->txtimer, + STMMAC_COAL_TIMER(tx_coal_timer), + HRTIMER_MODE_REL); + else + hrtimer_try_to_cancel(&tx_q->txtimer); } /**