Re: [Xen-devel] [PATCH net v2] xen-netback: Fix handling of skbs requiring too many slots

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jun 04, 2014 at 07:58:51PM +0100, Zoltan Kiss wrote:
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action 
> is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that 
> triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used 
> in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> (XEN_NETIF_MAX_TX_SIZE + 1) / PAGE_SIZE data slots (excluding the optional GSO
> slot, it doesn't carry data, therefore irrelevant in this case), as the 
> provided
> buffers are fully utilized.
> 

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Minor nit below.

[...]
> @@ -602,10 +611,14 @@ static void xenvif_rx_action(struct xenvif *vif)
>  
>               /* To avoid the estimate becoming too pessimal for some
>                * frontends that limit posted rx requests, cap the estimate
> -              * at MAX_SKB_FRAGS.
> +              * at MAX_SKB_FRAGS. In this case netback will fully coalesce
> +              * the skb into the provided slots.
>                */
> -             if (max_slots_needed > MAX_SKB_FRAGS)
> +             if (max_slots_needed > MAX_SKB_FRAGS) {
>                       max_slots_needed = MAX_SKB_FRAGS;
> +                     XENVIF_RX_CB(skb)->full_coalesce = true;
> +             } else
> +                     XENVIF_RX_CB(skb)->full_coalesce = false;
>  

Please enclose this line with {}, which is required by kernel coding
style.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel