[PATCH 7/7] ARM: tegra30: cpuidle: add LP2 driver for CPU0

Peter De Schrijver pdeschrijver at nvidia.com
Thu Oct 18 05:24:40 EDT 2012

On Tue, Oct 16, 2012 at 07:03:43PM +0200, Stephen Warren wrote:
> On 10/16/2012 02:06 AM, Peter De Schrijver wrote:
> >>> Even though we have plan to use coupled cpuidle, I still prefer to go
> >>> with the LP2 driver first. Then adding one more patch to support coupled
> >>> cpuidle based on LP2 driver. This is good for history. And if there is
> >>> any issue, it's more easy to roll back to the stable one.
> >>
> >> I don't think that implementing it one way and then changing to a
> >> different way will benefit history at all. It'll make the history more
> >> complicated. What exactly is the problem with just using coupled cpuidle
> >> from the start? If we did merge this implementation now, then switch to
> >> coupled cpuidle later, when do you think the switch would happen?
> > 
> > Before we consider doing this, I think we should have some idea on how
> > frequently we run into the situation where CPU0 is idle but a secondary
> > core is not. Depending on that we can then decide how useful coupled cpuidle
> > would be for us.
> Would it not be 75% of the time where we have 1 of 4 CPUs active? At
> least, that's assuming that all work is evenly distributed amongst CPUs,
> and hence it's random which CPU is the last to go idle, but perhaps
> that's not the case if CPU0 is somehow special workload-wise?

Depends, at least it used to be possible to tune the scheduler to prefer
CPU0 if the workload can run on a single CPU.



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