From: Nazim Amirul Calling hrtimer_start() on an already-active txtimer is unnecessary and expensive. Skip the restart if the timer is already active by adding an hrtimer_active() check before hrtimer_start(). Previously, each packet reset the timer to tx_coal_timer in the future, acting as a sliding window that delayed NAPI under burst traffic. With this change, an already-active timer is left to fire sooner, scheduling NAPI within tx_coal_timer of the first packet and freeing TX descriptors earlier. There is no race concern: hrtimer_start() is internally serialized and safe to call on an active timer. In the event of a race between hrtimer_active() and hrtimer_start(), the worst case is calling hrtimer_start() on an already-active timer, which is identical to the pre-patch behaviour. Performance on Cyclone V with dwmac-socfpga (iperf3 -u -b 0 -l 64): Before: ~45200 pps After: ~52300 pps (~15% improvement) Additionally, ~10% improvement in UDP throughput observed on Agilex5, with hrtimer CPU usage reduced from ~8% to ~0.6%. Signed-off-by: Rohan G Thomas Tested-by: Maxime Chevallier Reviewed-by: Maxime Chevallier Reviewed-by: Jacob Keller Signed-off-by: Nazim Amirul --- Changes in v3: - Corrected commit message to accurately describe timer behaviour change: timer now fires sooner under burst traffic, not "unchanged" (Andrew Lunn) - Added Reviewed-by from Jacob Keller Changes in v2: - Expanded commit message to address race condition concern and clarify tx_coal_timer semantics (Andrew Lunn) - Added performance numbers to commit message (Andrew Lunn) - Added Agilex5 performance data with hrtimer CPU usage improvement - Added Tested-by and Reviewed-by from Maxime Chevallier --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions() diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index 3591755ea30b..35da51c26248 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -3341,12 +3341,14 @@ static void stmmac_tx_timer_arm(struct stmmac_priv *priv, u32 queue) * 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 + if (unlikely(!napi_is_scheduled(napi))) { + if (unlikely(!(hrtimer_active(&tx_q->txtimer)))) + hrtimer_start(&tx_q->txtimer, + STMMAC_COAL_TIMER(tx_coal_timer), + HRTIMER_MODE_REL); + } else { hrtimer_try_to_cancel(&tx_q->txtimer); + } } /** -- 2.43.7