r8169: improve rtl8169_start_xmit (41294e6a) · Commits · 戴 / test

Improve the following in rtl8169_start_xmit: - tp->cur_tx can be accessed in parallel by rtl_tx(), therefore annotate the race by using WRITE_ONCE - avoid checking stop_queue a second time by moving the doorbell check - netif_stop_queue() uses atomic operation set_bit() that includes a full memory barrier on some platforms, therefore use smp_mb__after_atomic to avoid overhead Signed-off-by:

Heiner Kallweit <hkallweit1@gmail.com> Link: https://lore.kernel.org/r/80085451-3eaf-507a-c7c0-08d607c46fbc@gmail.com Signed-off-by:

Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/realtek/r8169_main.c

+6 −9

Original line number	Diff line number	Diff line
		@@ -4226,7 +4226,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
		/* rtl_tx needs to see descriptor changes before updated tp->cur_tx */
		smp_wmb();

		tp->cur_tx += frags + 1;
		WRITE_ONCE(tp->cur_tx, tp->cur_tx + frags + 1);

		stop_queue = !rtl_tx_slots_avail(tp, MAX_SKB_FRAGS);
		if (unlikely(stop_queue)) {
		@@ -4235,13 +4235,6 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
		*/
		smp_wmb();
		netif_stop_queue(dev);
		door_bell = true;
		}

		if (door_bell)
		rtl8169_doorbell(tp);

		if (unlikely(stop_queue)) {
		/* Sync with rtl_tx:
		* - publish queue status and cur_tx ring index (write barrier)
		* - refresh dirty_tx ring index (read barrier).
		@@ -4249,11 +4242,15 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
		* status and forget to wake up queue, a racing rtl_tx thread
		* can't.
		*/
		smp_mb();
		smp_mb__after_atomic();
		if (rtl_tx_slots_avail(tp, MAX_SKB_FRAGS))
		netif_start_queue(dev);
		door_bell = true;
		}

		if (door_bell)
		rtl8169_doorbell(tp);

		return NETDEV_TX_OK;

		err_dma_1:

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