From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Dual Core vs. Dual CPU Date: Mon, 24 Apr 2006 00:07:38 -0400 Message-ID: <444C4F0A.3070808@tmr.com> References: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-smp-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Urs Thuermann Cc: linux-smp@vger.kernel.org Urs Thuermann wrote: >I'd like to know what is the difference between a system with a dual >core CPU compared to two (single core) CPUs. I know dual core means >two CPUs on one chip, but is it really two complete CPUs or do they >share some component which is used by both CPU cores? > >For example HT duplicates only those parts of CPU which hold the state >of the program in execution (i.e. program counter, registers, etc.) >but they share the execution logic which often leads to performance >loss. > >Is there some performance difference between dual core and two real >CPUs, too? I assume the dual cores on one chip must share the bus >interface, but since in a multi CPU system only one CPU can access the >bus at a time, I think this doesn't make a performance difference, >right? > >Can anybody give some clarifiactions on these issue? > The bad part is that the cores share a bus connection, the good part is that it appears that some IPC can be done on chip. RELATED: has anyone done a measurements on the 955 chip, which is dual core and HT? On heavily threaded or parallel tasks I find 20-30% drop in clock time for HT processors, but I wonder if the CPU runs out of memory bandwidth. My standard test is a kernel compile. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979