Re: [PATCHSET] Announce: High-res timers,tickless/dyntick and dynamic HZ -V4

[Robert Hancock]

Ingo Molnar wrote:
> * Thomas Gleixner <tglx@xxxxxxxxxxx> wrote:
>
> > > Disabling NO_HZ and high resolution timers due to timer broadcasting
> > >
> > > Not sure exactly what this is indicating or what's triggered this, but 
> > > I'm assuming the patch isn't doing much on this machine?
> > The system is configured for SMP, but this is an UP machine and the 
> > APIC is disabled in the BIOS. Linux uses then the PIT and an IPI 
> > mechanism to broadcast timer events. We need to do the event 
> > reprogramming per CPU, so we switch off in that situation.
>
> hm, we should update the message to be less cryptic. Something like:
>
>   'Disabling NO_HZ and high resolution timers due to no APIC'
>
> and in this particular case we should also finetune the condition a bit 
> and make it conditional on the number of CPUs. I.e. if someone boots an 
> SMP kernel on a UP box we should still allow the PIT. (there wont be any 
> broadcasting done) [the only exception would be if CONFIG_HOTPLUG_CPU is 
> specified - in that case we cannot be sure whether a new CPU will be 
> plugged in or not]

Yes, I would say that this case should be handled better, considering 
this configuration is the default one for Fedora kernels, for one..

--
Robert Hancock      Saskatoon, SK, Canada
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Home Page: http://www.roberthancock.com/

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