netdev - Re: [PATCH] xen/netfront: improve truesize tracking

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Message-ID: <20121218141048.GC4518@phenom.dumpdata.com>
Date:	Tue, 18 Dec 2012 09:10:48 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	netdev@...r.kernel.org, Sander Eikelenboom <linux@...elenboom.it>,
	annie li <annie.li@...cle.com>, xen-devel@...ts.xensource.com
Subject: Re: [PATCH] xen/netfront: improve truesize tracking

On Tue, Dec 18, 2012 at 01:51:51PM +0000, Ian Campbell wrote:
> Using RX_COPY_THRESHOLD is incorrect if the SKB is actually smaller
> than that. We have already accounted for this in
> NETFRONT_SKB_CB(skb)->pull_to so use that instead.
> 
> Fixes WARN_ON from skb_try_coalesce.

This should probably be also on the stable tree for 3.7 at least?

> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Cc: Sander Eikelenboom <linux@...elenboom.it>
  ^^ - Reported-by: 

> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
  ^^ - Acked-by:

> Cc: annie li <annie.li@...cle.com>
> Cc: xen-devel@...ts.xensource.com
> Cc: netdev@...r.kernel.org
> Cc: stable@...nel.org # 3.7.x only
> ---
>  drivers/net/xen-netfront.c |   15 +++++----------
>  1 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..b06ef81 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -971,17 +971,12 @@ err:
>  		 * overheads. Here, we add the size of the data pulled
>  		 * in xennet_fill_frags().
>  		 *
> -		 * We also adjust for any unused space in the main
> -		 * data area by subtracting (RX_COPY_THRESHOLD -
> -		 * len). This is especially important with drivers
> -		 * which split incoming packets into header and data,
> -		 * using only 66 bytes of the main data area (see the
> -		 * e1000 driver for example.)  On such systems,
> -		 * without this last adjustement, our achievable
> -		 * receive throughout using the standard receive
> -		 * buffer size was cut by 25%(!!!).
> +		 * We also adjust for the __pskb_pull_tail done in
> +		 * handle_incoming_queue which pulls data from the
> +		 * frags into the head area, which is already
> +		 * accounted in RX_COPY_THRESHOLD.
>  		 */
> -		skb->truesize += skb->data_len - RX_COPY_THRESHOLD;
> +		skb->truesize += skb->data_len - NETFRONT_SKB_CB(skb)->pull_to;
>  		skb->len += skb->data_len;
>  
>  		if (rx->flags & XEN_NETRXF_csum_blank)
> -- 
> 1.7.2.5
> 
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