From owner-freebsd-hackers@FreeBSD.ORG  Mon Sep 12 14:41:56 2005
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
X-Original-To: freebsd-hackers@freebsd.org
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 0B9FA16A41F
	for <freebsd-hackers@freebsd.org>; Mon, 12 Sep 2005 14:41:56 +0000 (GMT)
	(envelope-from simon@comsys.ntu-kpi.kiev.ua)
Received: from comsys.ntu-kpi.kiev.ua (comsys.ntu-kpi.kiev.ua
	[195.245.194.142])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 7B92943D45
	for <freebsd-hackers@freebsd.org>; Mon, 12 Sep 2005 14:41:37 +0000 (GMT)
	(envelope-from simon@comsys.ntu-kpi.kiev.ua)
Received: from pm514-9.comsys.ntu-kpi.kiev.ua (pm514-9.comsys.ntu-kpi.kiev.ua
	[10.18.54.109]) (authenticated bits=0)
	by comsys.ntu-kpi.kiev.ua (8.12.10/8.12.10) with ESMTP id
	j8CEmv82012942
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
	Mon, 12 Sep 2005 17:48:58 +0300 (EEST)
Received: by pm514-9.comsys.ntu-kpi.kiev.ua (Postfix, from userid 1000)
	id 9CD411A3; Mon, 12 Sep 2005 17:38:26 +0300 (EEST)
Date: Mon, 12 Sep 2005 17:38:26 +0300
From: Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua>
To: Zlatan Ibrahimovic <razzorback2005@gmail.com>
Message-ID: <20050912143826.GA401@pm514-9.comsys.ntu-kpi.kiev.ua>
References: <e53d4aed05091012343a4b4882@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <e53d4aed05091012343a4b4882@mail.gmail.com>
User-Agent: Mutt/1.4.2.1i
X-Spam-Status: No, score=-4.0 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 
	autolearn=ham version=3.0.1
X-Spam-Checker-Version: SpamAssassin 3.0.1 (2004-10-22) on 
	comsys.ntu-kpi.kiev.ua
X-Virus-Scanned: ClamAV 0.82/1049/Wed Aug 31 10:19:01 2005 on
	comsys.ntu-kpi.kiev.ua
X-Virus-Status: Clean
Cc: freebsd-hackers@freebsd.org
Subject: Re: clock software interrupt
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>, 
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 12 Sep 2005 14:41:56 -0000

On Sat, Sep 10, 2005 at 09:34:48PM +0200, Zlatan Ibrahimovic wrote:
> Hi folks,
> I've seen clock software interrupt thread (referring to clk_ithd in
> kern/kern_intr.c); watching to manpages I read that priority is used
> as vector for that thread. My question is how can I call this software
> handler? There's no track in the IDT for the associated handler...
> (ia32, for better check see i386/i386/exception.s).

The softclock() function is registered as an another one handler
for SWI_CLOCK by calling the swi_add() function.  Since clk_ithd is
NULL at the moment when swi_add() for softclock() handler is called,
interrupt thread is created for SWI_CLOCK in swi_addr() by the
ithread_create() function.  An interrupt thread is a special kthread
and interrupt threads run ithread_loop() function as the main function
for kthread.  Interrupt handler for the softclock() function is returned
in softclock_ih.

The simplified idea of ithread_loop() is the following: if there is
the request for some handler, then process this request by requested
handler else voluntary switch context.

Another one handler for SWI_CLOCK is siopoll().  If you run
"ps auxw | grep clock" you will see two handlers for swi5
(SWI_CLOCK).

When hardclock() decides that softclock() should be called
is schedules clk_ithd ithread via handler softclock_ih by
calling swi_sched().