Re: [Xen-devel] [RFC PATCH 12/13] xen-netfront: implement TX persistent grants

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 12/05/15 18:18, Joao Martins wrote:
> Instead of grant/revoking the buffer related to the skb, it will use
> an already granted page and memcpy  to it. The grants will be mapped
> by xen-netback and reused overtime, but only unmapped when the vif
> disconnects, as opposed to every packet.
> 
> This only happens if the backend supports persistent grants since it
> would, otherwise, introduce the overhead of a memcpy on top of the
> grant map.
[...]
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
[...]
> @@ -1610,7 +1622,10 @@ static int xennet_init_queue(struct netfront_queue 
> *queue)
>       for (i = 0; i < NET_TX_RING_SIZE; i++) {
>               skb_entry_set_link(&queue->tx_skbs[i], i+1);
>               queue->grant_tx[i].ref = GRANT_INVALID_REF;
> -             queue->grant_tx[i].page = NULL;
> +             if (queue->info->feature_persistent)
> +                     queue->grant_tx[i].page = alloc_page(GFP_NOIO);

Need to check for alloc failure here and unwind correctly?

Why NOIO?

> +             else
> +                     queue->grant_tx[i].page = NULL;
>       }
>  
>       /* Clear out rx_skbs */
> 


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