netdev - Re: [RFC PATCH]: TCP + SACK + skb processing latency

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Date:	Fri, 1 Feb 2008 21:23:07 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Netdev <netdev@...r.kernel.org>
cc:	David Miller <davem@...emloft.net>
Subject: Re: [RFC PATCH]: TCP + SACK + skb processing latency

On Fri, 1 Feb 2008, Ilpo Järvinen wrote:

> @@ -1322,6 +1324,206 @@ static int tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
>  	return flag;
>  }
>  
> +/* Attempts to shift up to shiftlen worth of bytes from prev to skb.
> + * Returns number bytes shifted.
> + *
> + * TODO: in case the prev runs out of frag space, operation could be
> + * made to return with a partial result (would allow tighter packing).
> + */
> +static int skb_shift(struct sk_buff *prev, struct sk_buff *skb,
> +		     unsigned int shiftlen)
> +{
> +	int i, to, merge;
> +	unsigned int todo;
> +	struct skb_frag_struct *from, *fragto;
> +
> +	if (skb_cloned(skb) || skb_cloned(prev))
> +		return 0;
> +
> +	todo = shiftlen;
> +	i = 0;
> +	from = &skb_shinfo(skb)->frags[i];
> +	to = skb_shinfo(prev)->nr_frags;
> +
> +	merge = to - 1;
> +	if (!skb_can_coalesce(prev, merge + 1, from->page, from->page_offset))
> +		merge = -1;
> +	if (merge >= 0) {
> +		i++;
> +		if (from->size >= shiftlen)
> +			goto onlymerge;
> +		todo -= from->size;
> +	}
> +
> +	/* Skip full, not-fitting skb to avoid expensive operations */
> +	if ((shiftlen == skb->len) &&
> +	    (skb_shinfo(skb)->nr_frags - merge) < (MAX_SKB_FRAGS - to))

Before somebody else notices it:
  s/merge/i/, a leftover from flag -> idx conversion.

> +		return 0;
> +
> +	while (todo && (i < skb_shinfo(skb)->nr_frags)) {
> +		if (to == MAX_SKB_FRAGS)
> +			return 0;
> +


-- 
 i.