From owner-freebsd-current@FreeBSD.ORG  Wed Nov 24 08:40:54 2004
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 192F516A4CE; Wed, 24 Nov 2004 08:40:54 +0000 (GMT)
Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 6122943D2F; Wed, 24 Nov 2004 08:40:53 +0000 (GMT)
	(envelope-from phk@critter.freebsd.dk)
Received: from critter.freebsd.dk (localhost [127.0.0.1])
	by critter.freebsd.dk (8.13.1/8.13.1) with ESMTP id iAO8enU5061436;
	Wed, 24 Nov 2004 09:40:51 +0100 (CET)
	(envelope-from phk@critter.freebsd.dk)
To: Peter Jeremy <PeterJeremy@optushome.com.au>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 22 Nov 2004 18:31:32 +1100."
             <20041122073132.GW79646@cirb503493.alcatel.com.au> 
Date: Wed, 24 Nov 2004 09:40:49 +0100
Message-ID: <61435.1101285649@critter.freebsd.dk>
Sender: phk@critter.freebsd.dk
cc: arch@freebsd.org
cc: current@freebsd.org
Subject: Re: [REVIEW/TEST] nanodelay() vs DELAY() 
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 24 Nov 2004 08:40:54 -0000

In message <20041122073132.GW79646@cirb503493.alcatel.com.au>, Peter Jeremy wri
tes:

>The fact that this doesn't show up in the graph suggests that you're
>not using tc_nanodelay() at all within the 0..8usec range.

Right, but I can't trust that to be the case as CPUs get faster.

Originally I considered having MD routines registered also, stuff
like doing an "inb()" on i386 etc.  As it transpired the exponential
nature of the nanodelay_loopcall2() function makes this unnecessary.

>Your graph suggests that it's fairly good above about 200nsec even on
>equipment that is not blazingly fast.

Don't let the log-log scale deceive you.  being 50% wrong doesn't look
like much.

>Have you looked at the granularity of tc_nanodelay() (and the likely
>granularity required by callers)?  Is 8nsec reasonable given the
>inner loop of of tc_nanodelay()?

I'm actually considering making it 32nsec based on a 33MHz PCI speed.

>Do you have any idea where the transition points between the various
>delay functions are?

If you boot -v it will tell you.

>>The array takes up 9000 bytes on 32 bit and 17000 on 64 bit.
>
>AFAIK, all the FreeBSD architectures have 32-bit ints, so that should
>be 13,000 bytes for 64bit architectures.

Still, that's an awful lot for an old ass'y programmer like me :-)

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.