From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,7767a311e01e1cd
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news4.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!wns13feed!worldnet.att.net!attbi_s21.POSTED!53ab2750!not-for-mail
From: "Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>
Organization: jrcarter at acm dot org
User-Agent: Thunderbird 1.5.0.7 (Windows/20060909)
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: GNAT compiler switches and optimization
References: <OeF_g.1031657$084.91539@attbi_s22>
 <JOqdnWKamNaML6bYnZ2dnUVZ_oCdnZ2d@comcast.com>
In-Reply-To: <JOqdnWKamNaML6bYnZ2dnUVZ_oCdnZ2d@comcast.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Message-ID: <kUQ_g.114240$aJ.93653@attbi_s21>
NNTP-Posting-Host: 12.201.97.213
X-Complaints-To: abuse@mchsi.com
X-Trace: attbi_s21 1161550480 12.201.97.213 (Sun, 22 Oct 2006 20:54:40 GMT)
NNTP-Posting-Date: Sun, 22 Oct 2006 20:54:40 GMT
Date: Sun, 22 Oct 2006 20:54:40 GMT
Xref: g2news2.google.com comp.lang.ada:7144
Date: 2006-10-22T20:54:40+00:00
List-Id: <comp.lang.ada>

tmoran@acm.org wrote:
>    Each 800x800 Float matrix is about 2.5 megabytes so I would expect two
> threads to be fighting each other over the cache.  What are the single vs
> dual threaded times for, say, 250x250 arrays and a 1 MB cache on your
> machine, and on the dual Xeon machine?
>    Curiously, on a 3 GHz Pentium 4 with 1 MB cache and compiling
> with -O2 -gnatp using the venerable gnat 3.15p, I get
> Time:           8.511855190       800 1 thread
> Time:           5.682686332       800 2 threads
> for a speedup of 33%
> Time:           0.092724434       200 1 thread
> Time:           0.059209520       200 2 threads
> for a speedup of 36%

On my 3.2 GHz P4 HT (best of 3 runs), I get

Time:           0.170563050       250 1 thread
Time:           0.134637140       250 2 threads

for a speedup of 24%.

Time:           0.113739732       200 1 thread
Time:           0.070599932       200 2 threads

for a speedup of 36%.

I'm still only getting about 10% speedup for 800. Is it possible my 
cache is smaller?

-- 
Jeff Carter
"I unclog my nose towards you."
Monty Python & the Holy Grail
11