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On Tue, May 30, 2006 at 10:09:21AM +0200, Fabian Scheler wrote:Disable the caches. How long something takes to execute will depend on what is in the cache. If the code to be executed is still in the cache from the last time it was executied, it will execute a lot quicker than if it has to be fetches from RAM/ROM. The same applies to the data to be processed. So to be deterministic, you need to disable caches.
In order to guarantee deadlines, the worst case has to be deterministic, not the average case! In event-driven systems everything should be fine as long as your worst case response time is beneath your deadline, things get problematic when you use time-discrete algorithms, of course, but in this case you are better of using a time-driven approach, anyway.
So you at least need to disable caches when you determine what the worst case is, assuming the cache is actually helping you.
Andrew
-- Regards, Vamshi
------------------------------------------------- R.Vamshi Krishna, M.Tech. CSE (II year), IIT Bombay Room no. 320, A-wing, Hostel-12 Mobile : +919869781633 -------------------------------------------------
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