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!news3.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local01.nntp.dca.giganews.com!nntp.comcast.com!news.comcast.com.POSTED!not-for-mail NNTP-Posting-Date: Sun, 22 Oct 2006 13:01:53 -0500 From: tmoran@acm.org Newsgroups: comp.lang.ada Subject: Re: GNAT compiler switches and optimization References: X-Newsreader: Tom's custom newsreader Message-ID: Date: Sun, 22 Oct 2006 13:01:53 -0500 NNTP-Posting-Host: 67.164.83.70 X-Trace: sv3-pVjD3TKQQs1zv4x6Zx+Ngx9GRKu4bJIaDtg+AhbdDZACmhJStQLRB5VJIiJzD8rWW2uulAswi7eXfZw!sFEK3v8Jx+3D1P8zytTeIC/lRy6c4HCjjjM8fYX06aX52QeJiF8kMROKpSuEq7JzcT3p51LRZz3z!oJhwb0YQx/pF3A== X-Complaints-To: abuse@comcast.net X-DMCA-Complaints-To: dmca@comcast.net X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.32 Xref: g2news2.google.com comp.lang.ada:7137 Date: 2006-10-22T13:01:53-05:00 List-Id: > ... the time is much more than for the sequential > version, presumably due to cache effects. 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%