Re: [RFC] maximum latency tracking infrastructure

[Nick Piggin]

Arjan van de Ven wrote:
> Jesse Barnes wrote:
>
> > On Thursday, August 24, 2006 10:41 am, Arjan van de Ven wrote:
> >
> > > The reason for adding this infrastructure is that power management in
> > > the idle loop needs to make a tradeoff between latency and power
> > > savings (deeper power save modes have a longer latency to running code
> > > again).
> >
> >
> > What if a processor was already in a sleep state when a call to 
> > set_acceptable_latency() latency occurs? 
>
>
> there's nothing sane that can be done in that case; any wake up already 
> will cause the unwanted latency!
> A premature wakeup is only making it happen *now*, but now is as 
> inconvenient a time as any...
> (in fact it may be a worst case time scenario, say, an audio interrupt...)

Surely you would call set_acceptable_latency() *before* running such
operation that requires the given latency? And that set_acceptable_latency
would block the caller until all CPUs are set to wake within this latency.

That would be the API semantics I would expect, anyway.

--
SUSE Labs, Novell Inc.
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