From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <a5ec93342b820ee31072481987411c2f@gmx.de>
To: 9fans@9fans.net
Date: Mon, 23 Mar 2009 01:52:45 +0100
From: cinap_lenrek@gmx.de
In-Reply-To: <fb31fd1a5a64c0bf6f85af88838face3@quanstro.net>
MIME-Version: 1.0
Content-Type: multipart/mixed;
	boundary="upas-mpskxtmwvbhxhrgrggohomiqkp"
Subject: Re: [9fans] fossil periodic thread does zero sleep()
Topicbox-Message-UUID: c206131a-ead4-11e9-9d60-3106f5b1d025

This is a multi-part message in MIME format.
--upas-mpskxtmwvbhxhrgrggohomiqkp
Content-Disposition: inline
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit

I have no idea what HZ is used on my kernel, but i think
i understand the problem now.

I still can reproduce it with this:

	double t, ct, ts;

	ct = nsec()*1e-6;
	t = ct + msec;

	for(;;){
		ts = t - ct;
		sleep(ts);
		ct = nsec()*1e-6;
		if(t <= ct){
			t += msec;
		}
	}

The problem is that when sleep is a little bit too fast on every round,
t will never catch up with ct. so it sleeps shorter and shorter until
t - ct < 1.

It all works when changing t += msec to t = ct + msec. It may still
do a zero sleep, but the error will not add up.

making new kernel...

--
cinap

--upas-mpskxtmwvbhxhrgrggohomiqkp
Content-Type: message/rfc822
Content-Disposition: inline

Return-Path: <9fans-bounces+cinap_lenrek=gmx.de@9fans.net>
X-Flags: 0000
Delivered-To: GMX delivery to cinap_lenrek@gmx.de
Received: (qmail invoked by alias); 23 Mar 2009 00:30:10 -0000
Received: from gouda.swtch.com (EHLO gouda.swtch.com) [67.207.142.3]
  by mx0.gmx.net (mx104) with SMTP; 23 Mar 2009 01:30:10 +0100
Received: from localhost ([127.0.0.1] helo=gouda.swtch.com)
	by gouda.swtch.com with esmtp (Exim 4.67)
	(envelope-from <9fans-bounces@9fans.net>)
	id 1LlXzy-00053o-Ne; Mon, 23 Mar 2009 00:26:38 +0000
Received: from ladd.quanstro.net ([69.55.170.73])
	by gouda.swtch.com with esmtp (Exim 4.67)
	(envelope-from <quanstro@quanstro.net>) id 1LlXzw-00053j-Ji
	for 9fans@9fans.net; Mon, 23 Mar 2009 00:26:37 +0000
Message-ID: <fb31fd1a5a64c0bf6f85af88838face3@quanstro.net>
From: erik quanstrom <quanstro@quanstro.net>
Date: Sun, 22 Mar 2009 20:24:17 -0400
To: 9fans@9fans.net
In-Reply-To: <99a6e3a7cd4a1a6da9d06b97ddff4e37@gmx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Subject: Re: [9fans] fossil periodic thread does zero sleep()
X-BeenThere: 9fans@9fans.net
X-Mailman-Version: 2.1.9
Precedence: list
Reply-To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
List-Id: Fans of the OS Plan 9 from Bell Labs <9fans.9fans.net>
List-Unsubscribe: <http://mail.9fans.net/listinfo/9fans>,
	<mailto:9fans-request@9fans.net?subject=unsubscribe>
List-Archive: <http://mail.9fans.net/private/9fans>
List-Post: <mailto:9fans@9fans.net>
List-Help: <mailto:9fans-request@9fans.net?subject=help>
List-Subscribe: <http://mail.9fans.net/listinfo/9fans>,
	<mailto:9fans-request@9fans.net?subject=subscribe>
Sender: 9fans-bounces@9fans.net
Errors-To: 9fans-bounces+cinap_lenrek=gmx.de@9fans.net
X-GMX-Antivirus: 0 (no virus found)
X-GMX-Antispam: 0 (Mail was not recognized as spam)
X-GMX-UID: J+rxfi10bGI0JIYxzmRny1dncmZ1ZlyQ

what is your HZ set at?  after chasing a few bugs like this,
i've set HZ=1000.  actually i first saw the idea in sam hopins'
work  there's no performance drag and 1 ms
sleeps do actually sleep.

- erik
--upas-mpskxtmwvbhxhrgrggohomiqkp--