A different metric for scheduler optimisation

[Jamie Lokier]

Everyone who talk of the importance of cache reloads around context
switches should bear in mind:

  The typical run queue size is *not* the relevant figure.

The relevant question for scheduler optimisation is:

  `` What is the typical  (Switch Rate / Average Run Queue)  ratio?  ''


I'd be surprised if that doesn't support the current linear scan, but
the idea is worth some figures.

Does anyone have measurements that support this assertion: that most
apps which switch often have tiny run queues?


Davide Libenzi wrote:
> How many switch / sec will do a system with RQ << 1 ?
> Stay big say 500 ( keep this number in mind ).

A very good point.

> Take out another cache miss into the scheduler, multiply the time a
> cache miss takes for the number above ( 500 ), and weight it in one
> second.  What is Your improvement percent ?

You're right.  And a total guru for making your point in the face of
such adversity! :-)

have a radiant day,
-- Jamie

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