Re: [PATCH 0/6] RFC: CPU frequency min/max as PM QoS params

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On Thursday, January 12, 2012, Antti P Miettinen wrote:
> "Rafael J. Wysocki" <rjw@xxxxxxx> writes:
> >> By blocking sleep states we can address "system level latency" or "best case
> >> latency" but as far as I can see PM QoS does not address "worst case
> >> latency".
> >
> > I'm not sure what you mean by "worst case latency".
> 
> Umm.. the usual concept. If latency is the time from stimulus to
> response, this time can vary based on context. One part of the context
> is the hardware state but there is also the system load. So for example
> the time from interrupt to display being updated is affected by hardware
> state but also system load. As far as I understand, current PM QoS
> latency requests addresses hardware state but do not account for
> possible resource contention, e.g. several latency sensitive clients
> (device drivers, tasks) competing for CPU. In this sense minimum CPU
> frequency requests would be similar.

That's correct, we don't take possible contention into account in PM QoS,
because such conditions may happen idependently of power management anyway.

Thanks,
Rafael
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