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Regarding Multitasking on AIX

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HarpreetSachdeva

Programmer
Apr 11, 2003
25
GB
Please can any body tell what kind of multi tasking is done on AIX I mean that does AIX does pre-emptive multitasking or non premptive multitasking.


And if there any process that is taking to much of CPU time than how will OS will handle it that is according to my understanding if its time slice is over than it will be taken away and placed in the queue. And one more thing that if we run that CPU intensive process with low priority than will that help in releasing the CPU.

Thanks in adavance.
 
you should consult the AIX performance tuning guide, find it on the IBM library or redbook site.

IBM Certified -- AIX 4.3 Obfuscation
 
The multitasking in AIX is premptive (in the middle of a system call he is able to suspend it to answer an interrupt).

Regarding the scheduler, by default each thread (one process = at least one thread) gets a 10 ms timeslice, after which the dispatcher selects another thread from the runqueue, the one with the highest priority.

If there is an interruption, even if it did not have the full 10ms time-slice, the thread is suspended, the kernel answers the interrupt, and ANOTHER thread is dispatched on the CPU, this is the "default priority policy".

You can, by programmation, change this behaviour (in a fixed priority policy, a thread will alaways have the 10 ms timeslice, and if interrupted will be the next to be reschedulkd, eg oracle).

Some others scheduling policy are available but I don't remember exactly their names (something like round robin, ...).

Each time a thread gains the control of CPU, the C value associated with this thread is incremented (check the C column of ps -elf | more to check).

The more the C value is high, the more the process will be defavorized in priority re-calculation (every second).

Tools like schedtune (schedo on AIX 5.2) have some parameters on time-slice lenght and priority, but that's not very common to use them AFAIK.

regards

 
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