Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection

Peter Zijlstra
2015-11-05T14:33:38Z

On Thu, Nov 05, 2015 at 06:22:58AM -0800, Arjan van de Ven wrote:
> On 11/5/2015 2:09 AM, Peter Zijlstra wrote:
>
> >I can see such a scheme having a fairly big impact on latency, esp. with
> >forced idleness such as this. That's not going to be popular for many
> >workloads.
>
> idle injection is a last ditch effort in thermal management, before
> this gets used the hardware already has clamped you to a low frequency,
> reduced memory speeds, probably dimmed your screen etc etc.
>
> at this point there are 3 choices
> 1) Shut off the device
> 2) do uncoordinated idle injection for 40% of the time
> 3) do coordinated idle injection for 5% of the time
>
> as much as force injecting idle in a synchronized way sucks, the alternatives are worse.

OK, it wasn't put that way. I figured it was a way to use less power on
any workload with idle time on.

That said; what kind of devices are we talking about here; mobile with
pittyful heat dissipation? Surely a well designed server or desktop
class system should never get into this situation in the first place.