netdev - Re: [PATCH net-next] tcp:elapsed variable calculated twice while keepalive working

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Date:	Fri, 09 Aug 2013 14:06:39 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	tingw.liu@...il.com, netdev@...r.kernel.org, kuznet@....inr.ac.ru
Subject: Re: [PATCH net-next] tcp:elapsed variable calculated twice while
 keepalive working

On Fri, 2013-08-09 at 11:12 -0700, David Miller wrote:
> From: Tingwei Liu <tingw.liu@...il.com>
> Date: Tue,  6 Aug 2013 20:38:58 +0800
> 
> > When tcp keepalive working elapsed calculated twice while the first time is not needed!
> > 
> > CC: Eric Dumazet <eric.dumazet@...il.com>
> > CC: Alexey Kuznetsov <kuznet@....inr.ac.ru>
> > Signed-off-by: Tingwei Liu <tingw.liu@...il.com>
> 
> 
> Please put a space after "tcp:" in your Subject line prefixes, it looks
> awful the way you've done it here.
> 
> > @@ -591,11 +591,11 @@ static void tcp_keepalive_timer (unsigned long data)
> >  	if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
> >  		goto out;
> >  
> > -	elapsed = keepalive_time_when(tp);
> > -
> >  	/* It is alive without keepalive 8) */
> > -	if (tp->packets_out || tcp_send_head(sk))
> > +	if (tp->packets_out || tcp_send_head(sk)) {
> > +		elapsed = keepalive_time_when(tp);
> >  		goto resched;
> > +	}
> >  
> >  	elapsed = keepalive_time_elapsed(tp);
> 
> This is overkill, just delete the second assignment.  Your version makes
> the code look less elegant and also makes it harder to audit.
> --

As a matter of fact, 
keepalive_time_when(tp) and keepalive_time_elapsed(tp) are different ;)

This is very slow path in TCP stack, so it should not matter a lot.

 

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