Date: Tue, 10 Oct 2006 15:43:28 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-smp@freebsd.org Cc: JoaoBR <joao@matik.com.br> Subject: Re: Hyperthreading Issues (on Athlon64?) Message-ID: <200610101543.29138.jhb@freebsd.org> In-Reply-To: <200610101555.55558.joao@matik.com.br> References: <20061009114520.1355.qmail@web8608.mail.in.yahoo.com> <20061010181115.GB75278@lor.one-eyed-alien.net> <200610101555.55558.joao@matik.com.br>
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On Tuesday 10 October 2006 14:55, JoaoBR wrote: > On Tuesday 10 October 2006 15:11, Brooks Davis wrote: > > > My dmesg does not have the line about "Hyperthreading: 2 logical CPUs= ", > > > though. =A0But I had been pretty sure the Athlon64 chips didn't have = any > > > hyperthreading support. =A0Why is the HTT there? >=20 >=20 > HTT is NOT hyperthreading, HT is and HT does not exist on AMD64 Err, no. The HTT there stands for HyperThreading Technology. I should know as I added it. :) What it really means is that you can check one of the registers returned by cpuid 1 to see how many logical CPUs the current physical CPU package contains. Originally this was only used for hyperthreads, but it was reused for multi-core as well, so if you have a dual-core chip with 2 hyperthreads in each core, it reports 4 logical CPUs. If you have 2 cores, it reports 2 logical CPUs. If you have 1 core with 2 hyperthreads, it reports 2 logical CPUs. =2D-=20 John Baldwin
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