From owner-freebsd-hackers@FreeBSD.ORG  Tue Mar 30 16:43:50 2010
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 4EE2D106566B;
	Tue, 30 Mar 2010 16:43:50 +0000 (UTC) (envelope-from avg@icyb.net.ua)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
	by mx1.freebsd.org (Postfix) with ESMTP id 5C7B48FC0A;
	Tue, 30 Mar 2010 16:43:48 +0000 (UTC)
Received: from odyssey.starpoint.kiev.ua (alpha-e.starpoint.kiev.ua
	[212.40.38.101])
	by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id TAA28708;
	Tue, 30 Mar 2010 19:43:47 +0300 (EEST)
	(envelope-from avg@icyb.net.ua)
Message-ID: <4BB22A42.7050003@icyb.net.ua>
Date: Tue, 30 Mar 2010 19:43:46 +0300
From: Andriy Gapon <avg@icyb.net.ua>
User-Agent: Thunderbird 2.0.0.24 (X11/20100319)
MIME-Version: 1.0
To: John Baldwin <jhb@freebsd.org>
References: <4BACC791.70502@icyb.net.ua>
	<20100327214634.GI32799@server.vk2pj.dyndns.org>
	<86fx3k7jqi.fsf@ds4.des.no> <201003291044.28544.jhb@freebsd.org>
In-Reply-To: <201003291044.28544.jhb@freebsd.org>
X-Enigmail-Version: 0.95.7
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Cc: freebsd-hackers@freebsd.org,
	=?UTF-8?B?RGFnLUVybGluZyBTbcO4cmdyYXY=?= <des@des.no>
Subject: Re: periodically save current time to time-of-day hardware
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: Tue, 30 Mar 2010 16:43:50 -0000

on 29/03/2010 17:44 John Baldwin said the following:
> On Sunday 28 March 2010 7:45:25 am Dag-Erling Smørgrav wrote:
>> Peter Jeremy <peterjeremy@acm.org> writes:
>>> A new kthread which sleeps on channel "update_rtc".  When woken, it
>>> checks to see if it's within (say) 50msec of a second boundary and so,
>>> it does a trylock on the (new) RTC mutex.  If it grabs the mutex then
>>> it performs the update.  If it was too far from the second boundary or
>>> it fails to grab the mutex then it sleeps until the next second
>>> boundary and tries again.
>>>
>>> The existing resettodr() would then turn into a wakeup(update_rtc).
>> Sounds good to me, but if only that thread has access to the RTC, why
>> bother with a mutex?
> 
> I would dispense with the kthread and just use a callout (or have a callout 
> schedule a task for taskqueue_thread).

Guys,

do you think that periodic saving of system clock to hardware and making resettodr
asynchronous are dependent issues?  Or are they orthogonal and can be implemented
independently?

-- 
Andriy Gapon