netdev - Re: [RFC][PATCH 2/2] TCP: skip processing cached SACK blocks

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Message-ID: <Pine.LNX.4.64.0710081415020.31129@kivilampi-30.cs.helsinki.fi>
Date:	Mon, 8 Oct 2007 14:20:47 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	TAKANO Ryousei <takano@...-inc.co.jp>
cc:	Netdev <netdev@...r.kernel.org>, y-kodama@...t.go.jp
Subject: Re: [RFC][PATCH 2/2] TCP: skip processing cached SACK blocks

On Sun, 7 Oct 2007, TAKANO Ryousei wrote:
> From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
> > On Thu, 4 Oct 2007, TAKANO Ryousei wrote:
> > 
> > > @@ -1083,6 +1104,9 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
> > >  		int fack_count;
> > >  		int dup_sack = (found_dup_sack && (i == first_sack_index));
> > >  
> > > +		if (sack_block_skip[i])
> > > +			continue;
> > 
> > By doing this skipping here, you actually end up crippling lost_retrans 
> > detection even more than it was broken before. ...You probably didn't just 
> > notice that during tests because of unrelated suboptimal behavior (in 
> > fastpath_skb_hint handling). ...Anyway, correctness of this should be 
> > evaluated against the fixed lost_retrans, rather than the already 
> > broken one.
> 
> You can find the result that the average goodput slightly improves
> against the only PATCH #1 (fixed lost_retrans) applied kernel.

...Yeah, sorry, I was mistaken when the slow-path is taken and when it's 
not, thought that the old (current) fastpath_skb_hint code was more 
intelligent than it currently is... :-) That continue should not be
a problem.


-- 
 i.