Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932703AbVKYRhk (ORCPT ); Fri, 25 Nov 2005 12:37:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932705AbVKYRhk (ORCPT ); Fri, 25 Nov 2005 12:37:40 -0500 Received: from smtp.osdl.org ([65.172.181.4]:11669 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S932703AbVKYRhj (ORCPT ); Fri, 25 Nov 2005 12:37:39 -0500 Date: Fri, 25 Nov 2005 09:33:13 -0800 (PST) From: Linus Torvalds To: Chris Wedgwood cc: Alan Cox , "H. Peter Anvin" , Andi Kleen , Gerd Knorr , Dave Jones , Zachary Amsden , Pavel Machek , Andrew Morton , Linux Kernel Mailing List , Zwane Mwaikambo , Pratap Subrahmanyam , Christopher Li , "Eric W. Biederman" , Ingo Molnar Subject: Re: [patch] SMP alternatives In-Reply-To: <20051125073854.GA16771@taniwha.stupidest.org> Message-ID: References: <438359D7.7090308@suse.de> <1132764133.7268.51.camel@localhost.localdomain> <20051123163906.GF20775@brahms.suse.de> <1132766489.7268.71.camel@localhost.localdomain> <4384AECC.1030403@zytor.com> <1132782245.13095.4.camel@localhost.localdomain> <20051125073854.GA16771@taniwha.stupidest.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2320 Lines: 49 On Thu, 24 Nov 2005, Chris Wedgwood wrote: > > CPUs in embedded the space could outnumber desktops & servers greatly > (cell phones, access pointers, routers, media players, etc). Most of > these will be UP for some time. That's not entirely clear either. There are definite advantages to SMP even in the embedded space - or, to put it more strongly: _especially_ in the embedded space. Not only does power usage go up cubically with frequency (which means that two cores are a lot more efficient than one at double the frequency), but embedded space also often has some clear separation between tasks that -can- be threaded (and often part of is has real-time characteristics, so getting a core of its own can be a good thing). Often more so than in the desktop space. Now, obviously, in the "4- or 8-bit microcontroller" kind of embedded space, SMP isn't going to be a big issue. But anything that already uses an ARM, MIPS or a PowerPC-like chip, going SMP is not at all ridiculous. That includes things like cellphones, where one core might be for communication functions, and one for smartphones. None of the cellphone manufacturers seem to be in the least interested in doing a "phone only" solution. They can already do that cheaply, they can't make much money off it, and they are all interested in features. And it really _is_ more power-efficient to have, say, a dual-core 200MHz chip than it is to have a single-core 300MHz one. Now, sometimes those SMP systems will actually be used as "tightly coupled UP", where one of the CPU's is just basically a DSP. And from a power efficiency standpoint, having specialized hardware (and thus _A_MP rather than SMP) is obviously better, but in complex tasks - and communication tends to be that - general-purpose is often desirable enough that people will take the inefficiencies of a GP CPU over a fixed-function specialized DSP-kind of environment. But SMP is absolutely _not_ unusual in embedded. It's been there for years already, and it's clearly moving downwards there too. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/