Date: Thu, 8 Mar 2001 13:26:58 -0600 (CST) From: Chris Dillon <cdillon@wolves.k12.mo.us> To: Jeroen Ruigrok/Asmodai <asmodai@wxs.nl> Cc: <kris@obsecurity.org>, <jkh@FreeBSD.ORG>, <cvs-all@FreeBSD.ORG> Subject: Re: -march considered harmful? (Re: cvs commit: src/etc/defaults make.conf) Message-ID: <Pine.BSF.4.32.0103081314590.34818-100000@mail.wolves.k12.mo.us> In-Reply-To: <20010308102441.B7727@daemon.ninth-circle.org>
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CCs trimmed.... On Thu, 8 Mar 2001, Jeroen Ruigrok/Asmodai wrote: > -On [20010307 22:00], Jordan Hubbard (jkh@osd.bsdi.com) wrote: > >If you and Mr Hartman can conclusively prove that his problems were > >NOT caused by this then I'll discard the other whisperings I've heard > >and agree that the reason is not "demonstrable" here. > > FYI, I have been building two boxes at home with -march=pentium for the > past few weeks and have, aside from the usual CURRENT breakage, never > noted any binary problems being caused by setting -march. -O2 and > higher on the other hand... > > [Oh, and two STABLE boxes with -march=pentium] I'm now running several production boxes, as well as both of my desktop boxes, with either -march=pentium or -march=pentiumpro optimizations, and haven't noticied any problems yet. Out of curiosity though, can -march=pentium optimizations actually _hurt_ performance on PentiumPro-and-above machines? If I remember what I read correctly, Intel goofed on part of the P6 architecture and caused a partial register stall during what they actually recommended as an optimization for the P5 series CPUs in their optimization documents (duh?!). I think this is one reason why many people said "legacy code may actually run slower on the Pentium Pro" when it came out. I'm wondering if the same optimization is used by gcc. In the same vein, can -march=pentiumpro hurt performance for P5 class CPUs, or even cause the code not to work at all (unsupported instructions)? -- Chris Dillon - cdillon@wolves.k12.mo.us - cdillon@inter-linc.net FreeBSD: The fastest and most stable server OS on the planet. For IA32 and Alpha architectures. IA64, PPC, and ARM under development. http://www.freebsd.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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