netdev - Re: FYI - TCP/IP thin stream latency

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Message-ID: <Pine.LNX.4.64.0810290125300.7092@wrl-59.cs.helsinki.fi>
Date:	Mon, 24 Nov 2008 16:00:16 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	shemminger@...tta.com, doug.leith@...m.ie,
	Netdev <netdev@...r.kernel.org>
Subject: Re: FYI - TCP/IP thin stream latency

I'll post this rexmit combining again along with the other
tcp changes... Commenting your concerns below.

On Tue, 28 Oct 2008, David Miller wrote:

> Small error:
> 
> > +static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
> > +{
> > +	if (tcp_skb_pcount(skb) > 1)
> > +		return 0;
> > +	/* Once recombining for SACK completes this check could be made
> > +	 * less strict by reusing those parts.
> > +	 */
> > +	if (skb_shinfo(skb)->nr_frags != 0)
> > +		return 0;
> > +	if (skb_cloned(skb))
> > +		return 0;
> > +	if (skb == tcp_send_head(sk))
> > +		return 0;
> > +	/* Some heurestics for collapsing over SACK'd could be invented */
> > +	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
> > +		return 0;
> > +
> > +	return 1;
> > +}
> 
> For the "skb === tcp_send_head()" test, we're not interested if
> "skb" is equal, but rather whether next_skb is equal.

But that's what's actually happening... We'll terminate the loop
at that skb where it matches without doing any useful work for it,
so I'm just using a different way of "saying" the same as you.

> But the structure looks fine and when you send me a tested version
> of this patch I'll apply it to net-next-2.6, thanks!

Tested along with the other recombining things posting in couple of
minutes.

-- 
 i.
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