netdev - Re: Re: Re: Re: limited network bandwidth with 3.2.x kernels

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Date:	Tue, 21 Feb 2012 19:41:23 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	alekcejk@...glemail.com, netdev@...r.kernel.org
Subject: Re: Re: Re: Re: limited network bandwidth with 3.2.x kernels

Le vendredi 17 février 2012 à 11:41 -0500, Neal Cardwell a écrit :
> On Thu, Feb 16, 2012 at 5:35 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > An incoming skb is considered as "good citizen" in term of memory usage
> > if its truesize is no more than
> > len + len/4   (if adv_win_scale == 2)
> >
> > That was true when truesize was 1500+NET_SKB_PAD+sizeof(sk_buff),
> > but not true anymore when truesize is 2048+sizeof(sk_buff), or even more
> > when its 4096+sizeof(sk_buff)
> >
> > So receiver doesnt increase rcv_ssthresh and cannot open its window.
> >
> > tcp_grow_window() should be tweaked to :
> >
> > 1) Relax the requirements
> > 2) Allow bigger increase in case of super packets (LRO/GRO)
> 
> That sounds great. Is this something you're planning on tackling?
> 

Hmm, I thought about following (untested) patch :

Idea is to increase rcv_sshthresh by 2*len * (len/truesize), instead of
2*mss.



diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 53c8ce4..3fcea17 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -327,11 +327,17 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 		/* Check #2. Increase window, if skb with such overhead
 		 * will fit to rcvbuf in future.
 		 */
-		if (tcp_win_from_space(skb->truesize) <= skb->len)
-			incr = 2 * tp->advmss;
-		else
-			incr = __tcp_grow_window(sk, skb);
+		if (tp->rx_opt.rcv_wscale) {
+			u64 scaled = (u64)skb->len * skb->len;
 
+			do_div(scaled, skb->truesize >> 1);
+			incr = (int)scaled;
+		} else {
+			if (tcp_win_from_space(skb->truesize) <= skb->len)
+				incr = 2 * tp->advmss;
+			else
+				incr = __tcp_grow_window(sk, skb);
+		}
 		if (incr) {
 			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
 					       tp->window_clamp);



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