netdev - Re: TSO trimming question

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Message-Id: <20071220.035621.147230372.davem@davemloft.net>
Date:	Thu, 20 Dec 2007 03:56:21 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	netdev@...r.kernel.org, herbert@...dor.apana.org.au,
	jheffner@....edu
Subject: Re: TSO trimming question

From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Thu, 20 Dec 2007 13:40:51 +0200 (EET)

> [PATCH] [TCP]: Fix TSO deferring
> 
> I'd say that most of what tcp_tso_should_defer had in between
> there was dead code because of this.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>

Yikes!!!!!

John, we've been living a lie for more than a year. :-/

On the bright side this explains a lot of small TSO frames I've been
seeing in traces over the past year but never got a chance to
investigate.

> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 8dafda9..693b9f6 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1217,7 +1217,8 @@ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
>  		goto send_now;
>  
>  	/* Defer for less than two clock ticks. */
> -	if (!tp->tso_deferred && ((jiffies<<1)>>1) - (tp->tso_deferred>>1) > 1)
> +	if (tp->tso_deferred &&
> +	    ((jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
>  		goto send_now;
>  
>  	in_flight = tcp_packets_in_flight(tp);
--
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