From owner-freebsd-performance@FreeBSD.ORG  Thu Jan  3 02:46:48 2008
Return-Path: <owner-freebsd-performance@FreeBSD.ORG>
Delivered-To: freebsd-performance@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 6914316A418;
	Thu,  3 Jan 2008 02:46:48 +0000 (UTC)
	(envelope-from brde@optusnet.com.au)
Received: from mail05.syd.optusnet.com.au (mail05.syd.optusnet.com.au
	[211.29.132.186])
	by mx1.freebsd.org (Postfix) with ESMTP id DB4F113C459;
	Thu,  3 Jan 2008 02:46:47 +0000 (UTC)
	(envelope-from brde@optusnet.com.au)
Received: from c211-30-219-213.carlnfd3.nsw.optusnet.com.au
	(c211-30-219-213.carlnfd3.nsw.optusnet.com.au [211.30.219.213])
	by mail05.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id
	m032khu6028452
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO);
	Thu, 3 Jan 2008 13:46:45 +1100
Date: Thu, 3 Jan 2008 13:46:43 +1100 (EST)
From: Bruce Evans <brde@optusnet.com.au>
X-X-Sender: bde@delplex.bde.org
To: Gary Stanley <gary@velocity-servers.net>
In-Reply-To: <20080102123902.8CB6213C448@mx1.freebsd.org>
Message-ID: <20080103134118.G16729@delplex.bde.org>
References: <20071201205609.GA54238@harmless.hu>
	<20071204130810.GA77186@harmless.hu>
	<47779AA7.2060801@FreeBSD.org> <20071230132451.GA61295@harmless.hu>
	<47779EBC.5020900@FreeBSD.org> <20071230134354.GA63555@harmless.hu>
	<4777A65C.8020406@FreeBSD.org> <20071230141118.GA67574@harmless.hu>
	<4777AB9C.1010003@FreeBSD.org> <flb6bp$8kq$1@ger.gmane.org>
	<8cb6106e0801012008q18830aebp906ebfeb3c519e5a@mail.gmail.com>
	<477B6EB3.50202@FreeBSD.org>
	<20080102123902.8CB6213C448@mx1.freebsd.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: josh.carroll@gmail.com, Kris Kennaway <kris@freebsd.org>,
	freebsd-performance@freebsd.org, Ivan Voras <ivoras@freebsd.org>
Subject: Re: mysql scaling questions
X-BeenThere: freebsd-performance@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Performance/tuning <freebsd-performance.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-performance>,
	<mailto:freebsd-performance-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-performance>
List-Post: <mailto:freebsd-performance@freebsd.org>
List-Help: <mailto:freebsd-performance-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-performance>,
	<mailto:freebsd-performance-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 03 Jan 2008 02:46:48 -0000

On Wed, 2 Jan 2008, Gary Stanley wrote:

> At 06:00 AM 1/2/2008, Kris Kennaway wrote:
>
>> Per later discussion you will also need to either comment out the syscalls 
>> that are (might be) being cached by glibc to artificially inflate its 
>> reported rate, or verify that it is not doing so.
>
> IIRC linux uses vsyscalls on x86_64, and calling things like gettimeofday() 
> isn't as expensive as it normally should be.. vsyscalls are similar to 
> darwins' commpage.

How does it implement gettimeofday()'s 1us precision using direct access?
I see one way: put the time and other volatiles on an unmapped page, and
update the time in the trap handler.  With a lot of work, this should
be only slightly slower than the gettimeofday() syscall.

Bruce