Date: Tue, 10 Feb 2004 16:37:08 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Wes Peters <wes@softweyr.com> Cc: Juan Tumani <jtumani55@hotmail.com> Subject: Re: FreeBSD 5.2 v/s FreeBSD 4.9 MFLOPS performance (gcc3.3.3 v/s gcc2.9.5) Message-ID: <20040210223708.GC44504@dan.emsphone.com> In-Reply-To: <200402101129.34337.wes@softweyr.com> References: <BAY12-F37zmBUw7MurD00010899@hotmail.com> <200402101129.34337.wes@softweyr.com>
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In the last episode (Feb 10), Wes Peters said: > On Monday 09 February 2004 13:20, Juan Tumani wrote: > > I have an Intel D845GE m/b w/ a P4 1.7 CPU and I have the box setup > > to dual boot to either 4.9 or 5.2. Both OS are right off the > > latest posted iso CD image, i.e., no updates, no kernel tweaks, > > everything vanilla right out of the box. I compiled flops.c on > > both 4.9 and 5.2 and the 5.2 performance is less than half that of > > 4.9: 760 MFLOPS on 4.9 v/s 340 MFLOPS on 5.2. This sounds suspiciously like a stack alignment problem. Try running the following and see if your run times alternate between fast and slow every 4 runs: PAD= ; export PAD ; while : ; do ; PAD=z$PAD ; /usr/bin/time ./flops ; done Back in 2000, Bruce Evans posted the following patch that fixed the alignment problem on his system: http://www.freebsd.org/cgi/getmsg.cgi?fetch=438552+0+/usr/local/www/db/text/2000/freebsd-current/20000507.freebsd-current I don't believe either gcc 2.95 or 3.3 will align the stack themselves. icc does seem to. -- Dan Nelson dnelson@allantgroup.com
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