Messages in this thread | | | Date | Tue, 14 Feb 2012 02:14:45 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 |
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On 02/14/2012 01:55 AM, Srivatsa S. Bhat 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... >
Hmm.. interesting.. The only calls that ia64 uses which updates the num_online_cpus macro seem to be init_cpu_online(cpumask_of(0)); Atleast this is what the mainline code tells me (haven't checked linux-next).
So, if I am not mistaken, is the value of num_online_cpus() always 1 when Venki's patch is applied?
IOW, what output do you see from the following printk from arch/ia64/kernel/smpboot.c?
printk(KERN_INFO "Total of %d processors activated (%lu.%02lu BogoMIPS).\n", (int)num_online_cpus(), bogosum/(500000/HZ), (bogosum/(5000/HZ))%100);
Regards, Srivatsa S. Bhat
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