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cafa8804a4
Add patch fixing regression from stmmac TX timer. Refer to the single patch for extensive details on the problem. This should restore original performance before 4.19 kernel. Fixes: #11676 Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
77 lines
2.9 KiB
Diff
77 lines
2.9 KiB
Diff
From cd40cd8b1ca4a6f531c6c3fd78b306e5014f9c04 Mon Sep 17 00:00:00 2001
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From: Christian Marangi <ansuelsmth@gmail.com>
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Date: Mon, 18 Sep 2023 14:39:01 +0200
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Subject: [PATCH 3/4] net: stmmac: improve TX timer arm logic
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There is currently a problem with the TX timer getting armed multiple
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unnecessary times causing big performance regression on some device that
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suffer from heavy handling of hrtimer rearm.
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The use of the TX timer is an old implementation that predates the napi
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implementation and the interrupt enable/disable handling.
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Due to stmmac being a very old code, the TX timer was never evaluated
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again with this new implementation and was kept there causing
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performance regression. The performance regression started to appear
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with kernel version 4.19 with 8fce33317023 ("net: stmmac: Rework coalesce
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timer and fix multi-queue races") where the timer was reduced to 1ms
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causing it to be armed 40 times more than before.
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Decreasing the timer made the problem more present and caused the
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regression in the other of 600-700mbps on some device (regression where
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this was notice is ipq806x).
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The problem is in the fact that handling the hrtimer on some target is
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expensive and recent kernel made the timer armed much more times.
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A solution that was proposed was reverting the hrtimer change and use
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mod_timer but such solution would still hide the real problem in the
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current implementation.
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To fix the regression, apply some additional logic and skip arming the
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timer when not needed.
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Arm the timer ONLY if a napi is not already scheduled. Running the timer
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is redundant since the same function (stmmac_tx_clean) will run in the
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napi TX poll. Also try to cancel any timer if a napi is scheduled to
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prevent redundant run of TX call.
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With the following new logic the original performance are restored while
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keeping using the hrtimer.
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Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
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---
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.../net/ethernet/stmicro/stmmac/stmmac_main.c | 18 +++++++++++++++---
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1 file changed, 15 insertions(+), 3 deletions(-)
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--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
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+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
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@@ -2975,13 +2975,25 @@ static void stmmac_tx_timer_arm(struct s
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{
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struct stmmac_tx_queue *tx_q = &priv->dma_conf.tx_queue[queue];
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u32 tx_coal_timer = priv->tx_coal_timer[queue];
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+ struct stmmac_channel *ch;
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+ struct napi_struct *napi;
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if (!tx_coal_timer)
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return;
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- hrtimer_start(&tx_q->txtimer,
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- STMMAC_COAL_TIMER(tx_coal_timer),
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- HRTIMER_MODE_REL);
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+ ch = &priv->channel[tx_q->queue_index];
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+ napi = tx_q->xsk_pool ? &ch->rxtx_napi : &ch->tx_napi;
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+
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+ /* Arm timer only if napi is not already scheduled.
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+ * Try to cancel any timer if napi is scheduled, timer will be armed
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+ * again in the next scheduled napi.
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+ */
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+ if (unlikely(!napi_is_scheduled(napi)))
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+ hrtimer_start(&tx_q->txtimer,
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+ STMMAC_COAL_TIMER(tx_coal_timer),
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+ HRTIMER_MODE_REL);
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+ else
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+ hrtimer_try_to_cancel(&tx_q->txtimer);
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}
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/**
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