From owner-svn-src-all@FreeBSD.ORG  Fri Jan 20 00:46:12 2012
Return-Path: <owner-svn-src-all@FreeBSD.ORG>
Delivered-To: svn-src-all@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 82B54106564A;
	Fri, 20 Jan 2012 00:46:12 +0000 (UTC)
	(envelope-from listlog2011@gmail.com)
Received: from freefall.freebsd.org (freefall.freebsd.org
	[IPv6:2001:4f8:fff6::28])
	by mx1.freebsd.org (Postfix) with ESMTP id 6C65B8FC08;
	Fri, 20 Jan 2012 00:46:12 +0000 (UTC)
Received: from [127.0.0.1] (localhost [127.0.0.1])
	by freefall.freebsd.org (8.14.5/8.14.5) with ESMTP id q0K0k9J7045739;
	Fri, 20 Jan 2012 00:46:10 GMT (envelope-from listlog2011@gmail.com)
Message-ID: <4F18B951.6080404@gmail.com>
Date: Fri, 20 Jan 2012 08:46:09 +0800
From: David Xu <listlog2011@gmail.com>
User-Agent: Mozilla/5.0 (Windows NT 6.1;
	rv:9.0) Gecko/20111222 Thunderbird/9.0.1
MIME-Version: 1.0
To: Bruce Evans <brde@optusnet.com.au>
References: <201201160615.q0G6FE9r019542@svn.freebsd.org>
	<4F178CDC.3030807@gmail.com> <4F17B0DE.3060008@gmail.com>
	<201201191023.28426.jhb@freebsd.org>
	<20120120030456.O1411@besplex.bde.org>
In-Reply-To: <20120120030456.O1411@besplex.bde.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org, davidxu@FreeBSD.org,
	John Baldwin <jhb@FreeBSD.org>
Subject: Re: svn commit: r230201 - head/lib/libc/gen
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
Reply-To: davidxu@FreeBSD.org
List-Id: "SVN commit messages for the entire src tree \(except for &quot;
	user&quot; and &quot; projects&quot; \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 20 Jan 2012 00:46:12 -0000

On 2012/1/20 0:55, Bruce Evans wrote:
> On Thu, 19 Jan 2012, John Baldwin wrote:
>
>> On Thursday, January 19, 2012 12:57:50 am David Xu wrote:
>>> rdtsc() may not work on SMP, so I have updated it to use clock_gettime
>>> to get total time.
>>> http://people.freebsd.org/~davidxu/bench/semaphore2/
>>> <http://people.freebsd.org/%7Edavidxu/bench/semaphore2/>
>>>
>>> Still, lfence is a lot faster than atomic lock.
>
> I hope it does non-microbenchmarks.  IIRC, jhb found that it was
> actually slower in some cases.  I only did micro-benchmarks on Athlon64.

It depends on hardware, if it is a large machine with lots of cpu,
a small conflict on dual-core machine can become a large conflict
on large machine because it is possible more cpus are now
running same code which becomes a bottleneck. On a large machine
which has 1024 cores, many code need to be redesigned.