From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 16 Apr 2008 14:22:38 -0500 From: Jack Steiner Subject: Re: [PATCH] - Increase MAX_APICS for large configs Message-ID: <20080416192238.GA12115@sgi.com> References: <20080416163936.GA23099@sgi.com> <20080416184543.GD3722@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080416184543.GD3722@elte.hu> Sender: owner-linux-mm@kvack.org Return-Path: To: Ingo Molnar Cc: tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wed, Apr 16, 2008 at 08:45:43PM +0200, Ingo Molnar wrote: > > * Jack Steiner wrote: > > > Increase the maximum number of apics when running very large > > configurations. This patch has no affect on most systems. > > > > Signed-off-by: Jack Steiner > > > > I think this area of the code will be substantially changed when the > > full x2apic patch is available. In the meantime, this seems like an > > acceptible alternative. The patch has no effect on any 32-bit kernel. > > It adds ~4k to the size of 64-bit kernels but only if NR_CPUS > 255. > > ugly ... but well - applied. What's the static size cost of 64K APICs? 64k APICs would add ~8k to the static size of the kernel. Most of the increase is in the phys_cpu_present_map[]. When the x2apic patch is integrated, I expect (may be wrong) that this array will be eliminated since x2apic increases the max APIC_ID to 32 bits, Note that MAX_APICS is really misnamed. It is not the maximum number of APICs. It is the value of the largest APIC ID. IDs are not necessarily dense. --- jack -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org