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

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Ingo Molnar wrote:
* Thomas Gleixner <[email protected]> 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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