Satoru Takeuchi wrote:
>
> a) On sched_fork, the creator share its timeslice with new process.
> b) On sched_exit, if the exiting process didn't exhaust its first
> timeslice yet, it gives its timeslice to the parent.
>
> It has no problem on the process model since the creator is the parent.
> However, on the thread model, the creator is not the parent, it is same
> as the creator's parent. Hence, on this kind of program, the creator
> can't retrieve shared timeslice and exausts its timeslice at a rate of
> knots. In addition, somehow, the parent (typically shell?) gets extra
> timeslice.
Yes, this is an old oddity.
> I believe it's a bug and the exiting process should give its timeslice
> to the creator. Now I have some patch plan to fix this problem as follow:
>
> a) Add the field for the creator to task_struct. It needs extra memory.
... and locking/complications. The creator may already exited at this time.
> b) Doesn't add extra field and have thread's parent the creater, which is
> same as process creation. However it has many side effects, for example,
> we also need to change sys_getppid() implementation.
can't understand this, sorry.
Ingo, I think sched_exit() has another buglet,
if (unlikely(p->parent->time_slice > task_timeslice(p)))
p->parent->time_slice = task_timeslice(p);
should be
if (unlikely(parent->time_slice > task_timeslice(parent)))
parent->time_slice = task_timeslice(parent);
The
[PATCH 1/2] sched_exit: fix parent->time_slice calculation
http://marc.info/?l=linux-kernel&m=115101842505365
was dropped because "[PATCH 2/2]" was very wrong.
Could you look at it?
Oleg.
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