Messages in this thread |  | | | Date | Sat, 6 Jun 2009 18:18:55 +0200 (CEST) | | From | Thomas Gleixner <> | | Subject | Re: [PATCH] tick: add check for the existence of broadcast clock event device |
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On Sat, 6 Jun 2009, Thomas Gleixner wrote: > Feng, > > On Sat, 6 Jun 2009, Feng Tang wrote: > > > If your percpu devices are always on (not affected by C3 stop) then > > > you never dereference bc. So why do we need an extra check for !bc ? > > > > Hi tglx, > > > Thanks for the explanation. But we really ran into the NULL pointer > > case, in our platform, there are 2 X86 CPUs which have lapic, also > > it has 2 external timers which are pretty similar with HPET timers, > > those 2 external timers will be used as per-cpu timers (higher > > rating than lapic timer). In system's power cycle of suspend and > > resume, disable_nontboot_cpus will be called before goto suspend > > state,and enable_nonboot_cpus will be called for the resume process, > > so lapic timer of cpu1 will be first registered as per-cpu timer, > > and our external timer will be registered later after get a > > CPU_ONLINE notifier (similar with HPET), right in this time slot > > that lapic is the per-cpu timer, when system get the > > CLOCK_EVT_BROADCAST_ENTER/EXIT msg, tick_do_broadcast_on_off() is > > called and hit the NULL pointer case. > > Ok, I can understand now why we need it. I'll apply your patch and add > some more info into the commit msg so we do not look at it in a year > and scratch our heads. :)
Hmm, thought more about it.
1) How do you calibrate the local APIC timer if you do not have some initial timer device ?
2) If you have some initial timer device (PIT/HPET) why isn't it registered as broadcast device.
3) When the CPU uses the local APIC before the external timer is initialized what happens if the system goes into a deeper c-state ?
Thanks,
tglx
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