Messages in this thread |  | | Date | Mon, 13 Feb 2012 12:43:00 -0800 | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 | From | Venki Pallipadi <> |
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On Mon, Feb 13, 2012 at 12:25 PM, Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote: > On 02/14/2012 01:24 AM, Tony Luck wrote: > >> On Thu, Feb 2, 2012 at 12:03 PM, Rusty Russell <rusty@rustcorp.com.au> wrote: >>> IIRC playing with 3 archs boot code seemed like a recipe for disaster. >>> Feel free to try to fix this in -next though, and see what breaks... >> >> ia64 is what breaks ... well not actually broken ... but some very >> weird delays that >> show up in different places depending on whether this patch is present. >> >> First linux-next kernel to be blessed with this patch was >> next-20120210. Booting it >> I see: >> [ 7.164233] Switching to clocksource itc >> [ 146.077315] pnp: PnP ACPI init >> >> An ugly 138.913 second delay. Digging in the code showed that the bad bits >> happened inside stop_machine() >> >> Reverting just this patch makes this big delay disappear: >> >> [ 32.780232] Switching to clocksource itc >> [ 32.832100] pnp: PnP ACPI init >> >> but notice that it takes 25 extra seconds to get to this point in the >> boot (and while >> we expect to save some time by not re-computing num_online_cpus each time we >> need it ... this looks to be a lot more than I'd expect!) >> > > > Oh no!! ia64 directly uses cpu_set() and cpu_clear() on cpu_online_map!! > Grr.. It means num_online_cpus can be different from the actual number of > online cpus because it doesn't go through the set_cpu_online() path.. I haven't > yet pin-pointed the exact problem, but this definitely doesn't look good... >
This feels like a minefield in general. ia64, mips and um seems to have cpu_set and cpu_clear of cpu_online_map and/or cpu_possible_map in there. -- 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/
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