Re: [PATCH] O16int for interactivity

Nick Piggin
2003-08-18T15:44:14Z

Timothy Miller wrote:

>
>
> Con Kolivas wrote:
>
>>>
>>> A hardware timer interrupt happens at timeslice granularity. If the
>>> interrupt occurs, but the timeslice is not expired, then NORMALLY, the
>>> ISR would just return right back to the running task, but sometimes, it
>>> might decided to end the timeslice early and run some other task.
>>>
>>> Right?
>>
>>
>>
>> No, the timeslice granularity is a hard cut off where a task gets
>> rescheduled and put at the back of the queue again. If there is no
>> other task of equal or better priority it will just start again.
>
>
>
> Hmmm... I'm still having trouble making sense of this.
>
> So, it seems that you're saying that all tasks, regardless of
> timeslice length, are interrupted every 10ms (at 100hz).

Interrupted - in that scheduler_tick is run, yes. They don't get switched.

> If another task exists at a higher priority, then it gets run at
> that point.

Well loosely, yes. Actually, it happens if the task exists and is "running",
and has timeslice left. That only happens in scheduler_tick when the
current
task has finished its timeslice and the priority arrays are about to be
switched. The required conditions for preemption can also occur when a task
is being woken up, (after sleeping or newly forked).

> However, if there is more than one task at a given priority level,
> then they will not round-robin until the current task has used up all
> of its timeslice (some integer multiple of 10ms).

Thats right. Although I think Con or Ingo recently changed this in mm

>
>
> Am I finally correct, or do I still have it wrong? :)
>

Sounds right to me.