Messages in this thread |  | | | Date | Thu, 05 Aug 2004 12:09:50 +1000 | | From | Peter Williams <> | | Subject | Re: SCHED_BATCH and SCHED_BATCH numbering |
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Nick Piggin wrote: > Peter Williams wrote: > >> Albert Cahalan wrote: >> >>> Are these going to be numbered consecutively, or might >>> they better be done like the task state? SCHED_FIFO is >>> in fact already treated this way in one place. One might >>> want to test values this way: >>> >>> if(foo & (SCHED_ISO|SCHED_RR|SCHED_FIFO)) ... >>> >>> (leaving aside SCHED_OTHER==0, or just translate >>> that single value for the ABI) >>> >>> I'd like to see these get permenant allocations >>> soon, even if the code doesn't go into the kernel. >>> This is because user-space needs to know the values. >> >> >> >> Excellent idea. The definition of rt_task() could become: >> >> #define rt_task(p) ((p)->policy & (SCHED_RR|SCHED_FIFO)) >> >> instead of the highly dodgy:
I probably should have said "slightly" instead of "highly" here but I got carried away. :-)
>> >> #define rt_task(p) ((p)->prio < MAX_RT_PRIO) >> > > Nothing wrong with that, is there?
It's sloppy logic in that "prio" being less than MAX_RT_PRIO is a consequence of the task being real time not the definition of it. At the moment it is a sufficient condition for identifying a task as real time but that may not always be the case. But, the real issue is, what's the point of having a field, "policy", that IS the definitive indicator of the task's scheduling policy if you don't use it? An rt_task() function/macro defined in terms of the policy field with this suggested numbering scheme should always be correct.
At the moment rt_task(p) could be defined as ((p)->policy != SCHED_OTHER) but the addition of SCHED_ISO and SCHED_BATCH would break that. Another option would be (((p)->policy == SCHED_FIFO) || ((p)->policy == SCHED_RR)) but that's a little long winded and (avoiding it) is probably the reason for the current definition. So I stand by my comment that Albert's numbering scheme is an excellent idea. Peter -- Peter Williams pwil3058@bigpond.net.au
"Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce
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