Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932128AbWHGW1u (ORCPT ); Mon, 7 Aug 2006 18:27:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932201AbWHGW1u (ORCPT ); Mon, 7 Aug 2006 18:27:50 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:49059 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S932128AbWHGW1u (ORCPT ); Mon, 7 Aug 2006 18:27:50 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Adrian Bunk Cc: Andrew Morton , "Randy.Dunlap" , Andi Kleen , "Protasevich, Natalie" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig References: <20060807085924.72f832af.rdunlap@xenotime.net> <20060807105537.08557636.rdunlap@xenotime.net> <20060807194047.GM3691@stusta.de> Date: Mon, 07 Aug 2006 16:26:07 -0600 In-Reply-To: <20060807194047.GM3691@stusta.de> (Adrian Bunk's message of "Mon, 7 Aug 2006 21:40:48 +0200") Message-ID: User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) 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: 2220 Lines: 61 Adrian Bunk writes: > On Mon, Aug 07, 2006 at 12:53:35PM -0600, Eric W. Biederman wrote: >>... >> --- a/arch/x86_64/Kconfig >> +++ b/arch/x86_64/Kconfig >> @@ -384,6 +384,20 @@ config NR_CPUS >> This is purely to save memory - each supported CPU requires >> memory in the static kernel configuration. >> >> +config NR_IRQS >> + int "Maximum number of IRQs (224-57344)" > > int "Maximum number of IRQs (224-57344)" depends on SMP > > This way, people with SMP=n will not see this question. I doubt it will be interesting but it might be, it is certainly well defined what happens when you have more irqs that a cpu has irq destinations. >> + range 224 57344 >> + default "4096" if SMP >> + default "224" if !SMP > > Why not always > default "224" > ? A couple of reasons. - Things still need shaking out at the > 256 irq level and since this is going into -mm it is reasonable to have a large default. - It is silly to have a default that won't work on some hardware, that we can support without unreasonable overhead. - There are major simplicity gains to be had from a slight sparse irq space. - I haven't a clue what the irq numbers look like in the real world that we should be supporting since there was code in x86_64 and i386 to hack them up terribly. All I have a clue about are the really big machines. So I wouldn't be surprised if there were some small but I/O heavy machines that found 224 too limiting. I know of at least one uniprocessor machine that would have used almost all 224 irqs. - I want people to realize that we can easily have more than 256 irqs. With pure software interrupt sources and networking drivers allocating one irq per cpu the chances of us using our maximum allotment of irqs is much more likely in the next couple of years. - 4096 is the number I expect distribution vendors will ship. Why set a different default than what you expect most people will use? Eric - 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/