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r8169: improve rtl8169_start_xmit

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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>
This commit is contained in:
Heiner Kallweit 2020-11-14 21:49:53 +01:00 committed by Jakub Kicinski
parent 0064c5c1b3
commit 41294e6a43
1 changed files with 6 additions and 9 deletions
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15
drivers/net/ethernet/realtek/r8169_main.c
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@ -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 */ /* rtl_tx needs to see descriptor changes before updated tp->cur_tx */
smp_wmb(); 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); stop_queue = !rtl_tx_slots_avail(tp, MAX_SKB_FRAGS);
if (unlikely(stop_queue)) { if (unlikely(stop_queue)) {
@ -4235,13 +4235,6 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
*/ */
smp_wmb(); smp_wmb();
netif_stop_queue(dev); netif_stop_queue(dev);
door_bell = true;
}
if (door_bell)
rtl8169_doorbell(tp);
if (unlikely(stop_queue)) {
/* Sync with rtl_tx: /* Sync with rtl_tx:
* - publish queue status and cur_tx ring index (write barrier) * - publish queue status and cur_tx ring index (write barrier)
* - refresh dirty_tx ring index (read 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 * status and forget to wake up queue, a racing rtl_tx thread
* can't. * can't.
*/ */
smp_mb(); smp_mb__after_atomic();
if (rtl_tx_slots_avail(tp, MAX_SKB_FRAGS)) if (rtl_tx_slots_avail(tp, MAX_SKB_FRAGS))
netif_start_queue(dev); netif_start_queue(dev);
door_bell = true;
} }
if (door_bell)
rtl8169_doorbell(tp);
return NETDEV_TX_OK; return NETDEV_TX_OK;
err_dma_1: err_dma_1: