From 41294e6a434d4f19e957c55b275ea0324f275009 Mon Sep 17 00:00:00 2001
From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Sat, 14 Nov 2020 21:49:53 +0100
Subject: [PATCH] r8169: improve rtl8169_start_xmit
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 | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 8910e900ec45e..940fc6590566f 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -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:
--
2.30.2