Re: TSO trimming question

[David Miller <davem@davemloft.net>]

From: "Ilpo_Järvinen" <ilpo.jarvinen@helsinki.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@helsinki.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);