Messages in this thread | | | Date | Wed, 4 Apr 2001 15:08:33 -0500 | From | Tim Walberg <> | Subject | Re: kernel/sched.c questions |
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On 04/04/2001 16:52 -0300, Sardañons, Eliel wrote: >> Hello, I would like to know why you put this two functions: >> void scheduling_functions_start_here(void) { } >> ... >> void scheduling_functions_end_here(void) { } >>
That one I have no idea about - maybe some perverse sort of comment? Or maybe something somewhere needs to know the address range that some functions lie within, and these functions would delimit that range. Of course, that presumes that the compiler in use doesn't reorder functions in the object code that emits, but I think that's a fairly safe assumption for now...
>> why you put 'case TASK_RUNNING' >> >> switch (prev->state) { >> case TASK_INTERRUPTIBLE: >> if (signal_pending(prev)) { >> prev->state = TASK_RUNNING; >> break; >> } >> default: >> del_from_runqueue(prev); >> case TASK_RUNNING: >> } >>
This just indicates that there is nothing to be done for the TASK_RUNNING case - if it were left out, the default case would be taken. Of course, a 'case TASK_RUNNING: break;' placed earlier in the switch construct would be semantically the same, but there may be reasons related to code optimization that this was done the way it was.
>> and the last one: >> >> in the function schedule() you always use this syntax: >> >> ----- >> if (a_condition) >> goto bebe; >> bebe_back >> >> >> bebe: >> do_bebe(); >> goto bebe_back; >> ------ >> why not just doing: >> >> if (a_condition) >> do_bebe(); >> >> >> I know that goto's are better but finaly you are jumping to a function and >> then calling the function. I think you can improve performance doing this.
This looks like a hand-optimization to avoid a branch in the most common case. Chances are a_condition is supposed to be pretty rare, and the code you suggest would usually include a branch for the usual code path, then.
tw
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