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- From 2d1a42cf7f77cda54dbbee18d00b1200e7bc22aa Mon Sep 17 00:00:00 2001
- From: Christian Marangi <[email protected]>
- Date: Wed, 18 Oct 2023 14:35:48 +0200
- Subject: [PATCH 1/3] 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 <[email protected]>
- Signed-off-by: Paolo Abeni <[email protected]>
- ---
- .../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
- @@ -3003,13 +3003,25 @@ 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);
- }
-
- /**
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