From cd40cd8b1ca4a6f531c6c3fd78b306e5014f9c04 Mon Sep 17 00:00:00 2001 From: Christian Marangi Date: Mon, 18 Sep 2023 14:39:01 +0200 Subject: [PATCH 3/4] net: stmmac: improve TX timer arm logic 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(-) --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -2975,13 +2975,25 @@ static void stmmac_tx_timer_arm(struct s { 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); } /**