Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932582AbVKWWTm (ORCPT ); Wed, 23 Nov 2005 17:19:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932581AbVKWWTl (ORCPT ); Wed, 23 Nov 2005 17:19:41 -0500 Received: from smtp.osdl.org ([65.172.181.4]:45726 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S932583AbVKWWTk (ORCPT ); Wed, 23 Nov 2005 17:19:40 -0500 Date: Wed, 23 Nov 2005 14:19:08 -0800 (PST) From: Linus Torvalds To: Daniel Jacobowitz 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: <20051123214835.GA24044@nevyn.them.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> <20051123214835.GA24044@nevyn.them.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: 1391 Lines: 36 On Wed, 23 Nov 2005, Daniel Jacobowitz wrote: > > I don't think I see the point. This would let you optimize for the > "multi-threaded, but hasn't created any threads yet" or even > "multi-threaded, but not right now" cases. But those really aren't the > interesting case to optimize for - that's the equivalent of supporting > CPU hotplug. NO. There is not a _single_ compiler that is multi-threaded, and I'd argue that there probably never will be. It's pointless. There's a _lot_ of really performance-sensitive stuff that will NEVER EVER be threaded. You may run a hundred copies of them at the same time, but every single copy will be single-threaded. And this will optimize that case in a BIG way. This is _not_ about "CPU hotplug". This is _not_ about "threaded apps before they are threaded". This is all about the fact that serious computation is done single-threaded, and anybody who thinks that single-threading is going away is so totally out to lunch that it's not even fun. And yes, Sun will die. Single-thread performance matters a hell of a lot, and any company that bets that it doesn't, is a failure. 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/