Date: Thu, 28 Jul 2005 09:36:02 -0700 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: ray@redshift.com Cc: freebsd-amd64@freebsd.org Subject: Re: Benchmarks: AMD64 vs i386 on Dual 246 Opteron Message-ID: <20050728163602.GC64153@troutmask.apl.washington.edu> In-Reply-To: <3.0.1.32.20050728092338.01207628@pop.redshift.com> References: <3.0.1.32.20050728080526.00aa4098@pop.redshift.com> <86mzo7yvpe.fsf@xps.des.no> <3.0.1.32.20050728013152.00a4d188@pop.redshift.com> <86mzo7yvpe.fsf@xps.des.no> <3.0.1.32.20050728080526.00aa4098@pop.redshift.com> <3.0.1.32.20050728092338.01207628@pop.redshift.com>
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On Thu, Jul 28, 2005 at 09:23:38AM -0700, ray@redshift.com wrote: > | > | Drop 8 GB of memory into the box and see how the 32-bit > | FreeBSD performs in comparison to the 64-bit FreeBSD > | when your process consumes greater than 4GB of memory. > > True, once you go over the 4GB limit it's a different ball of wax. > However, until that time, it would be nice to get to the bottom of > why 64 bit code is running half the speed of 32 bit code on the exact > same machine - don't you think? Well, I have 12 GB of memory and run numerical intensive codes that easily can grab 4+ GB, so I've never explored i386 FreeBSD on an amd64 system. As mentioned elsewhere, I would look for optimizations within the software packages that target i386. Additionally, the instruction schedulers in gcc/gas have had many more years of development in comparison to the amd64 schedulers. An interesting test would be to build math/atlas on 32-bit and 64-bit FreeBSD and then run some linpack benchmarks. -- Steve
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