From owner-freebsd-arch@FreeBSD.ORG  Tue May 27 04:41:12 2003
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id D9C4237B401
	for <arch@freebsd.org>; Tue, 27 May 2003 04:41:12 -0700 (PDT)
Received: from cirb503493.alcatel.com.au (c18609.belrs1.nsw.optusnet.com.au
	[210.49.80.204])
	by mx1.FreeBSD.org (Postfix) with ESMTP id D315743F93
	for <arch@freebsd.org>; Tue, 27 May 2003 04:41:11 -0700 (PDT)
	(envelope-from peterjeremy@optushome.com.au)
Received: from cirb503493.alcatel.com.au (localhost.alcatel.com.au
	[127.0.0.1])h4RBfAp9044784;	Tue, 27 May 2003 21:41:10 +1000 (EST)
	(envelope-from jeremyp@cirb503493.alcatel.com.au)
Received: (from jeremyp@localhost)
	by cirb503493.alcatel.com.au (8.12.8/8.12.8/Submit) id h4RBfAMf044783;
	Tue, 27 May 2003 21:41:10 +1000 (EST)
Date: Tue, 27 May 2003 21:41:10 +1000
From: Peter Jeremy <peterjeremy@optushome.com.au>
To: Igor Sysoev <is@rambler-co.ru>
Message-ID: <20030527114110.GE44520@cirb503493.alcatel.com.au>
References: <20030527102806.GC44520@cirb503493.alcatel.com.au>
	<Pine.BSF.4.21.0305271513120.46491-100000@is>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Pine.BSF.4.21.0305271513120.46491-100000@is>
User-Agent: Mutt/1.4.1i
cc: arch@freebsd.org
Subject: Re: sendfile(2) SF_NOPUSH flag proposal
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussion related to FreeBSD architecture
	<freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 27 May 2003 11:41:13 -0000

On Tue, May 27, 2003 at 03:25:31PM +0400, Igor Sysoev wrote:
>On Tue, 27 May 2003, Peter Jeremy wrote:
>
>> 2) The new feature provides significant performance benefit.   In this
>>    case, I believe the overhead of calling setsockopt(2) is negligible
>>    so the performance gain would be negligible.
>
>I think the calling setsockopt(TCP_NOPUSH, 1) syscall has huge overhead
>as compared to several C operators inside sendfile(2).

Agreed.  But needing another one or two relatively cheap system calls
is negligible compared to the total overhead of accept(), several
select()/poll()/kqueue() calls, several sendfile() calls and a
close().  If you can produce some figures demonstrating that two
setsockopt() syscalls makes a noticable difference to the total cost
of sending a 48K file then your change might be worth considering.

>My point is not "the cheap change" but "the cheap overhead".

Please quantify the improvement amortised over a complete transaction
or connection.

Peter