From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 04 Jul 2003 09:18:12 -0700 From: "Martin J. Bligh" Subject: Re: 2.5.74-mm1 fails to boot due to APIC trouble, 2.5.73mm3 works. Message-ID: <13170000.1057335490@[10.10.2.4]> In-Reply-To: References: <20030703023714.55d13934.akpm@osdl.org> <3F054109.2050100@aitel.hist.no><20030704093531.GA26348@holomorphy.com> <20030704095004.GB26348@holomorphy.com><7910000.1057333295@[10.10.2.4]> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Zwane Mwaikambo Cc: William Lee Irwin III , Helge Hafting , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: > On Fri, 4 Jul 2003, Martin J. Bligh wrote: > >> Is it really necessary to turn half the apic code upside down in order >> to fix this? What's the actual bugfix that's buried in this cleanup? > > The way i see it is that you can't use NR_CPUS to determine the upper > bound on APIC IDs. e.g. my 3way is normally configured with NR_CPUS = 3 > but has APIC IDs of 0, 3 and 4. We need to make a distinction. Fair enough. But that would seem to be a simpler operation than this patch. >> > - if (i >= 0xf) >> > + if (i >= APIC_BROADCAST_ID) >> >> Is that always correct? it's not equivalent. > > Well we really want APIC_MAX_ID (or whatever it's called) Indeed. maybe MAX_PHYS_APIC_ID or something (it's different for logical). We break it out in subarch, but it's the same everywhere, which seems utterly useless - is probably historical cruft that needs to die. But that sounds like a separate issue, and a separate patch to me. >> > - for (bit = 0; kicked < NR_CPUS && bit < 8*sizeof(cpumask_t); bit++) { >> > + for (bit = 0; kicked < NR_CPUS && bit < MAX_APICS; bit++) { >> >> Is that the actual one-line bugfix this is all about? > > No, the problem is no space for physical ids in cpumask bitmaps, this > could manifest itself later on unless we fix it now. Ugh, are you saying the cpumask stuff shrinks masks to < 32 bits if NR_CPUS is low enough? If so, I can see more point to the patch, but it still seems like violent overkill. Stopping it doing that would probably fix it ... I can't imagine it buys you much. phys_cpu_present_map started off as an unsigned long, and I reused it in a fairly twisted way for NUMA-Q. As it's an array that's bounded by apic space, using the bios_cpu_apicid method that summit uses would be a much cleaner fix, and just leave the old one as a long bitmask like it used to be - which is fine for non- clustered apic systems, and saves inventing a whole new data type. See the cpu_present_to_apicid abstraction. >> Hmmmm. What are you using physical apicids here for? They seem >> irrelevant to this function. > > Urgh, it's really hard to determine what these functions really want half > the time. But that change does look wrong. Yeah, things taking logical apicids, and turning them into cpu numbers presumably shouldn't have to touch that. M. -- 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: aart@kvack.org