From owner-freebsd-arch@FreeBSD.ORG  Fri Dec  1 12:04:34 2006
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
X-Original-To: freebsd-arch@FreeBSD.org
Delivered-To: freebsd-arch@FreeBSD.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id 541DE16A403;
	Fri,  1 Dec 2006 12:04:34 +0000 (UTC) (envelope-from ivoras@fer.hr)
Received: from lara.cc.fer.hr (lara.cc.fer.hr [161.53.72.113])
	by mx1.FreeBSD.org (Postfix) with ESMTP id E8B0C43CAB;
	Fri,  1 Dec 2006 12:04:19 +0000 (GMT) (envelope-from ivoras@fer.hr)
Received: from [127.0.0.1] (localhost.cc.fer.hr [127.0.0.1])
	by lara.cc.fer.hr (8.13.8/8.13.8) with ESMTP id kB1C4Pa5016943;
	Fri, 1 Dec 2006 13:04:27 +0100 (CET) (envelope-from ivoras@fer.hr)
Message-ID: <45701A49.5020809@fer.hr>
Date: Fri, 01 Dec 2006 13:04:25 +0100
From: Ivan Voras <ivoras@fer.hr>
User-Agent: Thunderbird 1.5.0.4 (X11/20060625)
MIME-Version: 1.0
To: Robert Watson <rwatson@FreeBSD.org>
References: <20061119041421.I16763@delplex.bde.org>	<ejnvfo$tv2$1@sea.gmane.org>	<ek4gc8$492$1@sea.gmane.org>
	<20061126174041.V83346@fledge.watson.org>	<ekckpt$4h6$1@sea.gmane.org>
	<20061128142218.P44465@fledge.watson.org>
In-Reply-To: <20061128142218.P44465@fledge.watson.org>
X-Enigmail-Version: 0.94.0.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Cc: freebsd-arch@FreeBSD.org
Subject: Re: What is the PREEMPTION option good for?
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 01 Dec 2006 12:04:34 -0000

Robert Watson wrote:

> 
> They're independent twiddles, and can be frobbed separately.  If you can
> easily measure performance in the different configurations, seeing a
> table of permutations and results would be very nice to see what happens
> :-).

Ok, this is what I found:

- ipiwakeup doesn't produce differences as calculated by ministat
- turning off preemption produces visible differences, which are
calculated by ministat to be upto 10%.

x nopreempt+ipiwakeup
+ preempt+ipiwakeup
+--------------------------------------------------------------------------+
|+                + +        +                     x  x    xx    xx       x|
|    |___________A__M________|                       |______MA_______|     |
+--------------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   7         99.92        104.19        101.48     101.78429     1.4606717
+   4          90.5         95.78         94.12         93.53     2.2081365
Difference at 95.0% confidence
	-8.25429 +/- 2.4751
	-8.10959% +/- 2.43172%
	(Student's t, pooled s = 1.74576)


Sorry about the small number of samples - these are collected from the
system in the same state and product version (the machine was otherwise
idle, etc.), but the difference is always present - I've run simpler
benchmarks every few days since the discussion started and it's there.

This is on a low-end dual core Xeon (i.e. one socket, two cores, no HT),
enough RAM not to swap, requests/second with high concurrency on a web
application that does a lot of IPC to database & cache engines through
both TCP/localhost and unix sockets.