netdev - Re: [net-next PATCH v3 2/3] net: TCP thin linear timeouts

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Date:	Fri, 12 Feb 2010 06:19:13 -0500
From:	William Allen Simpson <william.allen.simpson@...il.com>
To:	Andreas Petlund <apetlund@...ula.no>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Ilpo Järvinen 
	<ilpo.jarvinen@...sinki.fi>, Eric Dumazet <eric.dumazet@...il.com>,
	Arnd Hannemann <hannemann@...s.rwth-aachen.de>,
	LKML <linux-kernel@...r.kernel.org>, shemminger@...tta.com,
	David Miller <davem@...emloft.net>, damian@....rwth-aachen.de
Subject: Re: [net-next PATCH v3 2/3] net: TCP thin linear timeouts

Last year, I'm pretty sure I was on record as thinking this is only a
marginally good idea, that would be better at the application layer.

Also that naming was a bit dicey.  Now the names are more descriptive,
but the "force" is a bit overkill.

How about?
   NET_TCP_FORCE_THIN_LINEAR_TIMEOUTS    -> NET_TCP_THIN_LINEAR_TIMEOUTS
   TCP_THIN_LT                           -> TCP_THIN_LINEAR_TIMEOUTS
   TCP_THIN_LT_RETRIES                   -> TCP_THIN_LINEAR_RETRIES
   tcp_force_thin_linear_timeouts        -> tcp_thin_linear_timeouts
   sysctl_tcp_force_thin_linear_timeouts -> sysctl_tcp_thin_linear_timeouts
   tp->thin_lt                           -> tp->thin_lto

The latter mostly traditional "to" for "timeout", as used most everywhere.

Andreas Petlund wrote:
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index de7d1bf..a682479 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -29,6 +29,7 @@ int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
>  int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
>  int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
>  int sysctl_tcp_orphan_retries __read_mostly;
> +int sysctl_tcp_force_thin_linear_timeouts __read_mostly;
>  
Where is the sysctl initialized?

> +	if ((tp->thin_lt || sysctl_tcp_force_thin_linear_timeouts) &&
> +	    tcp_stream_is_thin(sk) && sk->sk_state == TCP_ESTABLISHED &&
> +	    icsk->icsk_retransmits <= TCP_THIN_LT_RETRIES) {

Just for efficiency, I'd reorder this
   +	if (sk->sk_state == TCP_ESTABLISHED &&
   +	    (tp->thin_lt || sysctl_tcp_force_thin_linear_timeouts) &&
   +	    tcp_stream_is_thin(sk) &&
   +	    icsk->icsk_retransmits <= TCP_THIN_LT_RETRIES) {

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