RE: [Xen-devel] Power aware credit scheduler

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx] 
>Sent: 2008年6月19日 15:32
>
>
>> 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).

Yes, normally it's based at 20ms level.

>Does it then make sense to have the scheduler react to
>governor? Sounds like it could be a weird feedback loop.
>

Good suggestion. We're considering adding some more inputs from
key components into on-demand governor, instead of simply polling
busy ratio for freq change in a fixed interval. For example, when one
cpu pulls vcpu from other runqueues, it's the indicator that its current
freq may not fit and it's better to scale to max immediately instead 
of waiting for next 20ms check timer. Other indicators like interrupt,
event, etc. You kick a good instance. :-)

Thanks,
Kevin

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