netdev - Re: [PATCH net-next] net: qualcomm: rmnet: Support recycling frames to real device

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Date:   Fri, 27 Oct 2017 14:00:20 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: qualcomm: rmnet: Support recycling frames
 to real device

On Fri, Oct 27, 2017 at 1:30 PM, Subash Abhinov Kasiviswanathan
<subashab@...eaurora.org> wrote:
> For deaggregation, the real device receives a large linear skb and
> passes it on to rmnet. rmnet creates new skbs from this large frame.
>
> If the real device supports recycling, it does not need to allocate
> the large skbs during packet reception and can instead reuse them.
>
> Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
> ---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> index 29842cc..7869fcf 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> @@ -108,7 +108,10 @@ static void rmnet_set_skb_proto(struct sk_buff *skb)
>                 while ((skbn = rmnet_map_deaggregate(skb)) != NULL)
>                         __rmnet_map_ingress_handler(skbn, port);
>
> -               consume_skb(skb);
> +               if (skb->destructor)
> +                       skb->destructor(skb);
> +               else
> +                       consume_skb(skb);
>         } else {
>                 __rmnet_map_ingress_handler(skb, port);
>         }

This doesn't make sense to me, maybe I am missing something. What
"real device" is setting the skb->destructor() and doing it to somehow
handle recycling? The only driver I can find that is setting
skb->desctructor() is the Chelsio drivers, and they appear to be using
it to just clean-up DMA mappings in their transmit path.

Thanks.

- Alex