Re: [PATCH 5/7] igb: eliminate duplicate barriers on weakly-ordered archs

[Alexander Duyck]

On Tue, Mar 13, 2018 at 8:20 PM, Sinan Kaya  wrote:
> Code includes wmb() followed by writel(). 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 
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index b88fae7..ba8ccb5 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -8072,7 +8072,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 
> cleaned_count)
>  * such as IA-64).
>  */
> wmb();
> -   writel(i, rx_ring->tail);
> +   writel_relaxed(i, rx_ring->tail);
> }
>  }
>

This one missed the writel at the end of igb_tx_map().

Re: [PATCH 5/7] igb: eliminate duplicate barriers on weakly-ordered archs

[Alexander Duyck]

On Tue, Mar 13, 2018 at 8:20 PM, Sinan Kaya  wrote:
> Code includes wmb() followed by writel(). 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 
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index b88fae7..ba8ccb5 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -8072,7 +8072,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 
> cleaned_count)
>  * such as IA-64).
>  */
> wmb();
> -   writel(i, rx_ring->tail);
> +   writel_relaxed(i, rx_ring->tail);
> }
>  }
>

This one missed the writel at the end of igb_tx_map().

[PATCH 5/7] igb: eliminate duplicate barriers on weakly-ordered archs

[Sinan Kaya]

Code includes wmb() followed by writel(). 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 
---
 drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
b/drivers/net/ethernet/intel/igb/igb_main.c
index b88fae7..ba8ccb5 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -8072,7 +8072,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 
cleaned_count)
 * such as IA-64).
 */
wmb();
-   writel(i, rx_ring->tail);
+   writel_relaxed(i, rx_ring->tail);
}
 }
 
-- 
2.7.4

[PATCH 5/7] igb: eliminate duplicate barriers on weakly-ordered archs

[Sinan Kaya]

Code includes wmb() followed by writel(). 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 
---
 drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
b/drivers/net/ethernet/intel/igb/igb_main.c
index b88fae7..ba8ccb5 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -8072,7 +8072,7 @@ void igb_alloc_rx_buffers(struct igb_ring *rx_ring, u16 
cleaned_count)
 * such as IA-64).
 */
wmb();
-   writel(i, rx_ring->tail);
+   writel_relaxed(i, rx_ring->tail);
}
 }
 
-- 
2.7.4