netdev - Re: [RFC PATCH net-next 3/6] virtio-net: small optimization on free_old_xmit

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Date:	Wed, 15 Oct 2014 12:37:39 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	davem@...emloft.net, eric.dumazet@...il.com
Subject: Re: [RFC PATCH net-next 3/6] virtio-net: small optimization on
 free_old_xmit_skbs()

On Wed, Oct 15, 2014 at 03:25:27PM +0800, Jason Wang wrote:
> Accumulate the sent packets and sent bytes in local variables and perform a
> single u64_stats_update_begin/end() after.
> 
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Not sure how much it's worth but since Eric suggested it ...

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/net/virtio_net.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 3d0ce44..a4d56b8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -833,17 +833,21 @@ static void free_old_xmit_skbs(struct send_queue *sq)
>  	unsigned int len;
>  	struct virtnet_info *vi = sq->vq->vdev->priv;
>  	struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> +	u64 tx_bytes = 0, tx_packets = 0;
>  
>  	while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>  		pr_debug("Sent skb %p\n", skb);
>  
> -		u64_stats_update_begin(&stats->tx_syncp);
> -		stats->tx_bytes += skb->len;
> -		stats->tx_packets++;
> -		u64_stats_update_end(&stats->tx_syncp);
> +		tx_bytes += skb->len;
> +		tx_packets++;
>  
>  		dev_kfree_skb_any(skb);
>  	}
> +
> +	u64_stats_update_begin(&stats->tx_syncp);
> +	stats->tx_bytes += tx_bytes;
> +	stats->tx_packets =+ tx_packets;
> +	u64_stats_update_end(&stats->tx_syncp);
>  }
>  
>  static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> -- 
> 1.7.1
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