netdev - Re: [PATCH v3] net: batch skb dequeueing from softnet input_pkt

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Date:	Wed, 21 Apr 2010 16:23:05 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	jamal <hadi@...erus.ca>
Subject: Re: [PATCH v3] net: batch skb dequeueing from softnet input_pkt_queue

>        do {
> -               struct sk_buff *skb;
> +               lim = quota - work;
> +               if (lim > ARRAY_SIZE(sd->batch))
> +                       lim = ARRAY_SIZE(sd->batch);
> +               /* batch at most 16 buffers */
>

How about just using two input_pkt_queue's (define
input_pkt_queue[2])?  One that is used to enqueue from RPS, and one
that is being processed by process_backlog.  Then the only thing that
needs to be done under lock in process_backlog is to switch the
queues;  something like sd->current_input_pkt_queue ^= 1

Tom

> -               local_irq_disable();
>                rps_lock(sd);
> -               skb = __skb_dequeue(&sd->input_pkt_queue);
> -               if (!skb) {
> +               for (n = 0; n < lim; n++) {
> +                       sd->batch[n] = __skb_dequeue(&sd->input_pkt_queue);
> +                       if (!sd->batch[n])
> +                               break;
> +               }
> +               if (!sd->input_pkt_queue.qlen) {
>                        __napi_complete(napi);
> -                       rps_unlock(sd);
> -                       local_irq_enable();
> -                       break;
> +                       quota = 0;
>                }
> -               input_queue_head_incr(sd);
>                rps_unlock(sd);
> -               local_irq_enable();
>
> -               __netif_receive_skb(skb);
> -       } while (++work < quota);
> +               /* Now process our batch */
> +               for (i = 0; i < n; i++) {
> +                       skb = sd->batch[i];
> +                       /* flush_backlog() might have stolen this skb */
> +                       input_queue_head_incr(sd);
> +                       if (likely(skb)) {
> +                               sd->batch[i] = NULL;
> +                               local_irq_enable();
> +                               __netif_receive_skb(skb);
> +                               local_irq_disable();
> +                       }
> +               }
> +               work += n;
> +       } while (work < quota);
>
> +       local_irq_enable();
>        return work;
>  }
>
>
>
>
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