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ixgbevf: keep writel() closer to wmb()

PATCH New Sinan Kaya 2 participants 4 messages Mar 22, 2018 – Mar 23, 2018

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Sinan Kaya

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#0 lore raw

PATCH v5 1/2 ixgbevf: keep writel() closer to wmb()

Remove ixgbevf_write_tail() in favor of moving writel() close to wmb().

Signed-off-by Sinan Kaya <[email protected]>
---
 drivers/net/ethernet/intel/ixgbevf/ixgbevf.h      | 5 -----
 drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 6 +++---
 2 files changed, 3 insertions(+), 8 deletions(-)
drivers/net/ethernet/intel/ixgbevf/ixgbevf.h +0 -5
index f712646..f97091d 100644
@@ -312,11 +312,6 @@ static inline u16 ixgbevf_desc_unused(struct ixgbevf_ring *ring)
 	return ((ntc > ntu) ? 0 : ring->count) + ntc - ntu - 1;
 }
 
-static inline void ixgbevf_write_tail(struct ixgbevf_ring *ring, u32 value)
-{
-	writel(value, ring->tail);
-}
-
 #define IXGBEVF_RX_DESC(R, i)	\
 	(&(((union ixgbe_adv_rx_desc *)((R)->desc))[i]))
 #define IXGBEVF_TX_DESC(R, i)	\
drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c +3 -3
index 3d9033f..815cb1a 100644
@@ -725,7 +725,7 @@ static void ixgbevf_alloc_rx_buffers(struct ixgbevf_ring *rx_ring,
 		 * such as IA-64).
 		 */
 		wmb();
-		ixgbevf_write_tail(rx_ring, i);
+		writel(i, rx_ring->tail);
 	}
 }
 

@@ -1232,7 +1232,7 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
 		 * know there are new descriptors to fetch.
 		 */
 		wmb();
-		ixgbevf_write_tail(xdp_ring, xdp_ring->next_to_use);
+		writel(xdp_ring->next_to_use, xdp_ring->tail);
 	}
 
 	u64_stats_update_begin(&rx_ring->syncp);

@@ -4004,7 +4004,7 @@ static void ixgbevf_tx_map(struct ixgbevf_ring *tx_ring,
 	tx_ring->next_to_use = i;
 
 	/* notify HW of packet */
-	ixgbevf_write_tail(tx_ring, i);
+	writel(i, tx_ring->tail);
 
 	return;
 dma_error:
Signature · 1 line
2.7.4
author
#1 lore raw

PATCH v5 2/2 ixgbevf: eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel() in multiple places. writel() already has a barrier on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the register write.

Since code already has an explicit barrier call, changing writel() to writel_relaxed().

Signed-off-by Sinan Kaya <[email protected]>
---
 drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c +3 -3
index 815cb1a..eaa930e 100644
@@ -725,7 +725,7 @@ static void ixgbevf_alloc_rx_buffers(struct ixgbevf_ring *rx_ring,
 		 * such as IA-64).
 		 */
 		wmb();
-		writel(i, rx_ring->tail);
+		writel_relaxed(i, rx_ring->tail);
 	}
 }
 

@@ -1232,7 +1232,7 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
 		 * know there are new descriptors to fetch.
 		 */
 		wmb();
-		writel(xdp_ring->next_to_use, xdp_ring->tail);
+		writel_relaxed(xdp_ring->next_to_use, xdp_ring->tail);
 	}
 
 	u64_stats_update_begin(&rx_ring->syncp);

@@ -4004,7 +4004,7 @@ static void ixgbevf_tx_map(struct ixgbevf_ring *tx_ring,
 	tx_ring->next_to_use = i;
 
 	/* notify HW of packet */
-	writel(i, tx_ring->tail);
+	writel_relaxed(i, tx_ring->tail);
 
 	return;
 dma_error:
Signature · 1 line
2.7.4
#2 lore raw

PATCH v5 2/2 ixgbevf: eliminate duplicate barriers on weakly-ordered archs

Quoted 18 lines

-----Original Message-----
From: Intel-wired-lan [mailto:intel-wired-lan-bounces at osuosl.org] On Behalf Of Sinan Kaya
Sent: Thursday, March 22, 2018 8:43 AM
To: Kirsher, Jeffrey T <[email protected]>
Cc: sulrich at codeaurora.org; netdev at vger.kernel.org;
timur at codeaurora.org; linux-kernel at vger.kernel.org; Sinan Kaya <[email protected]>; intel-wired-lan at lists.osuosl.org; linux-arm- msm at vger.kernel.org; linux-arm-kernel at lists.infradead.org
Subject: [Intel-wired-lan] [PATCH v5 2/2] ixgbevf: eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel() in multiple places. writel() already has a barrier on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the register write.

Quoted 7 lines

Since code already has an explicit barrier call, changing writel() to writel_relaxed().

Signed-off-by Sinan Kaya <[email protected]>
---
 drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
Tested-by Andrew Bowers <[email protected]>
#3 lore raw

PATCH v5 1/2 ixgbevf: keep writel() closer to wmb()

In reply to Sinan Kaya
Quoted 12 lines

-----Original Message-----
From: Intel-wired-lan [mailto:intel-wired-lan-bounces at osuosl.org] On Behalf Of Sinan Kaya
Sent: Thursday, March 22, 2018 8:43 AM
To: Kirsher, Jeffrey T <[email protected]>
Cc: sulrich at codeaurora.org; netdev at vger.kernel.org; timur at codeaurora.org; linux-kernel at vger.kernel.org; Sinan Kaya <[email protected]>; intel-wired-lan at lists.osuosl.org; linux-arm- msm at vger.kernel.org; linux-arm-kernel at lists.infradead.org
Subject: [Intel-wired-lan] [PATCH v5 1/2] ixgbevf: keep writel() closer to wmb()

Quoted 7 lines

Remove ixgbevf_write_tail() in favor of moving writel() close to wmb().

Signed-off-by Sinan Kaya <[email protected]>
---
 drivers/net/ethernet/intel/ixgbevf/ixgbevf.h      | 5 -----
 drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 6 +++---
 2 files changed, 3 insertions(+), 8 deletions(-)
Tested-by Andrew Bowers <[email protected]>