Improving idle behavior in tickless systems [LWN.net]

Improving idle behavior in tickless systems

Posted Dec 31, 2018 21:37 UTC (Mon) by corbet (editor, #1)
In reply to: Improving idle behavior in tickless systems by rweikusat2
Parent article: Improving idle behavior in tickless systems

I'm sorry, but I think you're trying a little too hard here.

An individual interrupt is not predictable, but, as with the weather, a prediction that "things will happen in the future much like they have in the recent past" is relatively likely to be true. Interrupts are not quantum events, they are the result of the workload and the environment that the system is in. So there is value in a heuristic that looks at residency times and predicts that something similar will happen next.

Perhaps it's time to give this a rest?

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Improving idle behavior in tickless systems

Posted Dec 31, 2018 21:46 UTC (Mon) by rweikusat2 (subscriber, #117920) [Link] (1 responses)

The code still doesn't and cannot predict device interrupts. That's something the article simply got wrong. Some part of it is based on the assumption that an idle state shouldn't be used if more than 4 of the last 8 measured idle periods were shorter than its so-called target residency. There doesn't seem to be any published rationale for this design and small powers of 2 always raise the suspicion of someone picking a number from a hat.

This may well be a sensible heuristic but a heuristic it remains --- no fortune telling aka "prediction" involved.

Improving idle behavior in tickless systems

Posted Dec 31, 2018 23:48 UTC (Mon) by rahulsundaram (subscriber, #21946) [Link]

> This may well be a sensible heuristic but a heuristic it remains --- no fortune telling aka "prediction" involved.

Prediction != fortune telling. There are multiple meanings for the same word.

https://www.merriam-webster.com/dictionary/prediction

One of them is forecast which is defined as

"to calculate or predict (some future event or condition) usually as a result of study and analysis of available pertinent data"