Re: [Xen-devel] Power aware credit scheduler

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 19/6/08 05:51, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> b) when physical cpu resides in idle C-state
> Avoid unnecessary work to keep longer C-state residency.
> For example, accouting process (tick timer, more specifically)
> can be stopped before C-state entrance and then resumed after
> waking up. The point is that no accounting is required when current
> cpu is idle, and any runqueue change triggering from other cpus
> incurs a IPI to this cpu which effectively breaks it back to C0
> state with accounting resumed. Since the residency period may
> be longer than accouting period (30ms), csched_tick should be
> aware of resume event to adjust elapsed credits.

Yes, this should be an easy low-hanging fruit to fix.

> c) when cpu's freq is scaled dynamically
> When cpufreq/Px is enabled, cpu's frequency is adjusted
> to different operation points driven by a on-demand governor. So
> csched_acct may need take frequency difference among cpus into
> consideration and total available credits won't be a simple 300 *
> online cpu_number.

Not sure. I think the current governor runs frequently to react to the
scheduler (i.e., try to keep the CPU non-idle by downscaling frequency;
upscale frequency when the CPU gets busy; both these done over sub-second
timescales). Does it then make sense to have the scheduler react to
governor? Sounds like it could be a weird feedback loop.

 -- Keir



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