Messages in this thread | | | Date | Thu, 23 Mar 2000 21:52:19 -0300 (BRT) | From | Augusto Cesar Radtke <> | Subject | Re: general timing question |
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On Thu, 23 Mar 2000, Michael B. Rash wrote:
> > Suppose that I have a process that generates a timestamp every time it > loops through some task, and assume that this process is not running with > real time support. Is there any way to guarantee that the timestamping > will be accurate to within some bound? That is, my task ends at some > absolute time t0, and my timestamp gets assigned some short time t1 after > t0 (if there is a context switch before the timestamp is assigned then the > delay will be greater I guess). So, is there any way to bound t1-t0?
Disabling the interrupts could be a solution for your problem, I don't know if it's the best solution, but remember to make just the assigment with interrupts disabled, after it enable them.
> My guess is that trying to _guarantee_ that t1-t0 < n for some n would > be useless since my process could get swapped out with some higher > priority process, or a bunch of interrupts happen, etc. But on _average_ > what would n be? It would be related to the processor speed, the machine > load, and the jiffie that has been compiled into the machine correct?
Yes, t1, t0 and n should be in jiffies, all the internal kernel structures uses jiffies (wait queues, timers, bhs, etc). And the n value should be something like the time to processes 5-10 instructions.
-augusto
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