Subject: Re: [PATCH 2/2] mv643xx_eth: hook up skb recycling

From: Eric Dumazet <[email-masked]>
Date: Wed, 03 Sep 2008 16:25:34 +0200

Lennert Buytenhek a écrit :
> This increases the maximum loss-free packet forwarding rate in
> routing workloads by typically about 25%.
> 
> Signed-off-by: Lennert Buytenhek <[email-masked]>
>

Interesting...

>  	refilled = 0;
>  	while (refilled < budget && rxq->rx_desc_count < rxq->rx_ring_size) {
>  		struct sk_buff *skb;
>  		int unaligned;
>  		int rx;
>  
> -		skb = dev_alloc_skb(skb_size + dma_get_cache_alignment() - 1);
> +		skb = __skb_dequeue(&mp->rx_recycle);

Here you take one skb at the head of queue

> +		if (skb == NULL)
> +			skb = dev_alloc_skb(mp->skb_size +
> +					    dma_get_cache_alignment() - 1);
> +
>  		if (skb == NULL) {
>  			mp->work_rx_oom |= 1 << rxq->index;
>  			goto oom;
> @@ -600,8 +591,8 @@ static int rxq_refill(struct rx_queue *rxq, int budget)
>  			rxq->rx_used_desc = 0;
>  
>  		rxq->rx_desc_area[rx].buf_ptr = dma_map_single(NULL, skb->data,
> -						skb_size, DMA_FROM_DEVICE);
> -		rxq->rx_desc_area[rx].buf_size = skb_size;
> +						mp->skb_size, DMA_FROM_DEVICE);
> +		rxq->rx_desc_area[rx].buf_size = mp->skb_size;
>  		rxq->rx_skb[rx] = skb;
>  		wmb();
>  		rxq->rx_desc_area[rx].cmd_sts = BUFFER_OWNED_BY_DMA |
> @@ -905,8 +896,13 @@ static int txq_reclaim(struct tx_queue *txq, int budget, int force)
>  		else
>  			dma_unmap_page(NULL, addr, count, DMA_TO_DEVICE);
>  
> -		if (skb)
> -			dev_kfree_skb(skb);
> +		if (skb != NULL) {
> +			if (skb_queue_len(&mp->rx_recycle) < 1000 &&
> +			    skb_recycle_check(skb, mp->skb_size))
> +				__skb_queue_tail(&mp->rx_recycle, skb);
> +			else
> +				dev_kfree_skb(skb);
> +		}

Here you put a skb at the head of queue. So you use a FIFO mode.

To have best performance (cpu cache hot), you might try to use a LIFO mode (use __skb_queue_head()) ?

Could you give us your actual bench results (number of packets received per second, number of transmited packets per second), 
and your machine setup.

Thank you