Date: Fri, 17 Mar 2006 09:16:47 -0300 From: JoaoBR <joao@matik.com.br> To: Bruce Evans <bde@zeta.org.au> Cc: freebsd-amd64@freebsd.org Subject: Re: amd64 slower than i386 on identical AMD 64 system? / How is hyperthreading handled on amd64? Message-ID: <200603170916.48004.joao@matik.com.br> In-Reply-To: <20060317064348.C48622@delplex.bde.org> References: <20060313221836.5491916A420@hub.freebsd.org> <200603160917.30225.peter@wemm.org> <20060317064348.C48622@delplex.bde.org>
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On Thursday 16 March 2006 18:30, Bruce Evans wrote: > On Thu, 16 Mar 2006, Peter Wemm wrote: > > There are a number of weaknesses in the amd64 port too. In particular, > > the math library does not yet use the generally superior SSE2 > > instructions. This is a real setback because the ABI uses SSE2 > > floating point parameter passing. The effect is that some random libm > > function is given a SSE2 register, which we convert to and x87 fp stack > > register, do the x87 operation, then convert the x87 stack register > > back to a SSE2 register then return the SSE2 result. This is > > especially unfortunate when the native SSE2 instruction that would > > operate on the SSE2 registers directly is faster. But, I don't know > > SSE2 nor x87 fpu assembler code very well, so I've done "just enough" > > to get things to work. > do SSE influence "normal" operations as disk-io, memory access and network ? > My benchmarks in libm indicate that 64-bitness + SSE2 end up being a > tiny improvment for single precision and a signifcant improvement for > double and long double precision (even for long double where SSE2 > cannot be used!), but this is only for versions that doesn't use the > FPU for transcendental functions, and I think it is mainly from foot > shooting in the 32-bit versions. The improvment in double precision > is needed to be competitive with the hardware transcendental functions, > and the foot shooting is from heavy use of the GET/SET macros -- these > macros force things to memory and thus tend to cause pipeline stalls. > sorry, would you mind to say what do you mean with "foot shooting" here? Joćo A mensagem foi scaneada pelo sistema de e-mail e pode ser considerada segura. Service fornecido pelo Datacenter Matik https://datacenter.matik.com.brhome | help
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