Kernel Latency calibration Question

Howard Cai hcai at uvic.ca
Wed Jul 27 02:47:52 CEST 2005


Hi:

1. the kerenl latency testsuite report the max and acerage kernel latency by 
using
the periodic task scheduling (expected time and execution time) 
the average is usually a few hundres ns.

2. the calibration tool use similar means, and then report the average kernel
latnecy back, In this it report the kernel latency with "average + 
tuned.latency_8254" rather than the average, in used is tuned.latency_8254.

the average is usually a few hundreds as well. with + latency_8254, it would
be around 5300 ns. (4700ns for defined latency_8254)


3. Just got lost, how did the calculation average contain the 8254 latency? 
the 8254 timer is already used for one shot timer, so is the above calculation 
already haing the latency concerned?

4. does the average only mean scheduling latency?

5. the 8254 setup time is about 2000ns, what does latency_8254 contains 
(4700)?
I did not find the related routine for this calibration, it seem hard defined.


Please anybody  help to clarify?


Thanks,

Howard.






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