Messages in this thread |  | | Date | Tue, 14 Feb 2012 01:55:05 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 |
| |
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...
Regards, Srivatsa S. Bhat
|  |