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

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Date:	Thu, 16 Feb 2012 16:09:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	Netdev <netdev@...r.kernel.org>, alekcejk@...glemail.com
Subject: Re: limited network bandwidth with 3.2.x kernels

Le jeudi 16 février 2012 à 13:51 +0000, Ben Hutchings a écrit :

> I'm aware of this problem and I believe it exists with most
> implementations of LRO.
> 
> The out-of-tree version of the sfc driver has its own soft-LRO
> implementation (SSR) which does some limited connection tracking to
> detect slow start and disable aggregation temporarily.  I've been
> meaning to look into enhancing GRO to match SSR, but haven't got round
> to it yet.


Not sure why we cant change tcp_grow_window() to take into account
number of segments in skb ?

It currently increments rcv_ssthresh by a fixed amount (2 * advmss)

        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);
                inet_csk(sk)->icsk_ack.quick |= 1;
                }



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