netdev - Re: [bpf-next V2 PATCH 3/8] ixgbe: implement flush flag for ndo_xdp

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Date:   Mon, 4 Jun 2018 15:19:05 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     liu.song.a23@...il.com, songliubraving@...com,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [bpf-next V2 PATCH 3/8] ixgbe: implement flush flag for
 ndo_xdp_xmit

On 05/31/2018 10:59 AM, Jesper Dangaard Brouer wrote:
> When passed the XDP_XMIT_FLUSH flag ixgbe_xdp_xmit now performs the
> same kind of ring tail update as in ixgbe_xdp_flush.  The update tail
> code in ixgbe_xdp_flush is generalized and shared with ixgbe_xdp_xmit.
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |   20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 87f088f4af52..4fd77c9067f2 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -10022,6 +10022,15 @@ static int ixgbe_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>  	}
>  }
>  
> +static void ixgbe_xdp_ring_update_tail(struct ixgbe_ring *ring)
> +{
> +	/* Force memory writes to complete before letting h/w know there
> +	 * are new descriptors to fetch.
> +	 */
> +	wmb();
> +	writel(ring->next_to_use, ring->tail);
> +}

Did you double check that this doesn't become a function call? Should this
get an __always_inline attribute?

> +
>  static int ixgbe_xdp_xmit(struct net_device *dev, int n,
>  			  struct xdp_frame **frames, u32 flags)
>  {
> @@ -10033,7 +10042,7 @@ static int ixgbe_xdp_xmit(struct net_device *dev, int n,
>  	if (unlikely(test_bit(__IXGBE_DOWN, &adapter->state)))
>  		return -ENETDOWN;
>  
> -	if (unlikely(flags & ~XDP_XMIT_FLAGS_NONE))
> +	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
>  		return -EINVAL;
>  
>  	/* During program transitions its possible adapter->xdp_prog is assigned
> @@ -10054,6 +10063,9 @@ static int ixgbe_xdp_xmit(struct net_device *dev, int n,
>  		}
>  	}
>  
> +	if (unlikely(flags & XDP_XMIT_FLUSH))
> +		ixgbe_xdp_ring_update_tail(ring);
> +
>  	return n - drops;
>  }
>  
> @@ -10072,11 +10084,7 @@ static void ixgbe_xdp_flush(struct net_device *dev)
>  	if (unlikely(!ring))
>  		return;
>  
> -	/* Force memory writes to complete before letting h/w know there
> -	 * are new descriptors to fetch.
> -	 */
> -	wmb();
> -	writel(ring->next_to_use, ring->tail);
> +	ixgbe_xdp_ring_update_tail(ring);
>  
>  	return;
>  }
>