netdev - [net-next 4/6] igb: Use dma_wmb() instead of wmb() before doorbell writes

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Message-Id: <20180726174050.8923-5-jeffrey.t.kirsher@intel.com>
Date:   Thu, 26 Jul 2018 10:40:48 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     davem@...emloft.net
Cc:     Venkatesh Srinivas <venkateshs@...gle.com>, netdev@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com, jogreene@...hat.com,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net-next 4/6] igb: Use dma_wmb() instead of wmb() before doorbell writes

From: Venkatesh Srinivas <venkateshs@...gle.com>

igb writes to doorbells to post transmit and receive descriptors;
after writing descriptors to memory but before writing to doorbells,
use dma_wmb() rather than wmb(). wmb() is more heavyweight than
necessary before doorbell writes.

On x86, this avoids SFENCEs before doorbell writes in both the
tx and rx refill paths.

Signed-off-by: Venkatesh Srinivas <venkateshs@...gle.com>
Tested-by: Aaron Brown <aaron.f.brown@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index e3a0c02721c9..25720d95d4ea 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6031,7 +6031,7 @@ static int igb_tx_map(struct igb_ring *tx_ring,
 	 * We also need this memory barrier to make certain all of the
 	 * status bits have been updated before next_to_watch is written.
 	 */
-	wmb();
+	dma_wmb();
 
 	/* set next_to_watch value indicating a packet is present */
 	first->next_to_watch = tx_desc;
@@ -8531,7 +8531,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 cleaned_count)
 		 * applicable for weak-ordered memory model archs,
 		 * such as IA-64).
 		 */
-		wmb();
+		dma_wmb();
 		writel(i, rx_ring->tail);
 	}
 }
-- 
2.17.1