Date: Wed, 06 Jun 2007 12:47:59 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: freebsd-current@FreeBSD.ORG Cc: jroberson@chesapeake.net, almarrie@gmail.com Subject: Re: Intel C2D COREs not used equally in FreeBSD 7.0-CURRENT i386 Message-ID: <86ps49l5pc.fsf@dwp.des.no> In-Reply-To: <200706051316.l55DGSU0052272@lurza.secnetix.de> (Oliver Fromme's message of "Tue\, 5 Jun 2007 15\:16\:28 %2B0200 \(CEST\)") References: <200706051316.l55DGSU0052272@lurza.secnetix.de>
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Oliver Fromme <olli@lurza.secnetix.de> writes: > It's a common mistake to assume that amd64 only makes sense > if you have >=3D 4GB RAM. There are several reasons why it > might be useful to switch from i386 to amd64: > > - Most programs (though not all) will run faster, because > in amd64 mode there are twice as many general-purpose > registers, giving compilers much better opportunities > for optimizations and caching of values, and reducing > slow memory accesses. "twice as many" is an understatement. AMD64 has 16 GPRs vs i386's 8 if you consider BP, SI, DI and SP as GPRs (as the AMD and Intel literature does); in practical terms the score is 12 to 4. > - Some applications might benefit from a larger virtual > address space > 4 GB. (Note that this is not related > to the amount of physical RAM!) For instance, Varnish maps its entire storage into memory, and will benefit greatly from the increased address space. > In practice there's (almost) only one reason not to run > FreeBSD/amd64 on amd64-capable hardware: If you depend > on a certain piece of software which is known not to run > correctly in 64bit mode. Fortunately those are not many. The only one I can think of (for a desktop) is the Flash plugin. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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