On Mon, May 11, 2015 at 10:34:11PM +0300, Julian Anastasov wrote:
> On Mon, 11 May 2015, Peter Zijlstra wrote:
>
> > > - schedule_timeout_idle (instead of schedule_timeout call):
> > > __set_current_state(TASK_IDLE);
> > > return schedule_timeout(timeout);
> > >
> > > - we here are really idle, so "N" looks ok
> >
> > So I don't get the point of the schedule_timeout_*() stubs. What are
> > they for? Why would one use an unconditional schedule_timeout() call?
> > Isn't that what msleep() is for?
>
> msleep will not return until timeout has expired.
> Instead, we want to notice the kthread_should_stop() event
> immediately. Additionally, TASK_UNINTERRUPTIBLE will increase
> the load average. We can do it with extra wait queue
> and the new __wait_event_idle_timeout but I guess
> schedule_timeout_idle will be a good replacement for
> schedule_timeout_interruptible calls when used for kthreads.
Fair enough I suppose, but then calling it schedule*() is just plain
wrong, it does not behave/act like a normal schedule() call.
Lemme go look at how widely abused that is.
*sigh*, its all over the place :/
$ git grep "schedule_timeout_\(interruptible\|killable\|uninterruptible\)" | wc
-l
392
That said; I still don't see the point of schedule_timeout_idle(), we
should not sleep poll for state like that. We should only use TASK_IDLE
when we are in fact _IDLE_ and do not have work to do, at which point
one should use an wait_event() like construct to wait for new work.
> > + * like wait_event_timeout() -- except it uses TASK_IDLE to avoid loadavg
> > + */
> > +#define wait_event_idle_timeout(wq, condition, timeout)
> > \
> > +({ \
> > + long __ret = timeout; \
> > + might_sleep(); \
> > + if (!___wait_cond_timeout(condition)) \
> > + ret = __wait_event_idle_timeout(wq, condition, timeout);\
>
> ret may need underscores here...
I'm fairly sure that might aid in compilation indeed :-)
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