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

[Robert Hancock <hancockr@shaw.ca>]

Ingo Molnar wrote:
> * Thomas Gleixner <tglx@timesys.com> 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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