Messages in this thread | | | Date | Wed, 12 Apr 2017 12:43:09 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC][PATCH] sched: Have do_idle() call __schedule() without enabling preemption |
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On Wed, 12 Apr 2017 18:21:57 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Apr 12, 2017 at 10:41:24AM -0400, Steven Rostedt wrote: > > [ tl;dr; version ] > > > > Peter, In order to have synchronize_rcu_tasks() work, the idle task can > > never be preempted. There's a very small window in > > schedule_preempt_disable() that enables preemption, and when this > > happens, it breaks synchronize_rcu_tasks() (see above email for > > details). > > > > Is there any reason to enable preemption, or can we simply have idle > > call into schedule without ever allowing it to be preempted, as in my > > patch? > > Dunno,.. this changelog should convince me, not make me do the work :-)
I didn't want you to do any work. I was wondering if you knew of any reason. But looking into the history of the do_idle() function and schedule_preempt_disable(), I don't see any reason. I'll post another patch with a better change log.
> > > Note, it is almost good enough to just change > > schedule_preempt_disable() to do the exact same thing, but there's one > > instance in kernel/locking/mutex.c that calls it in a non running state. > > The point being that that must not happen because of > sched_submit_work(), which, for idle, should not matter.
Right, and also for all the other cases that call schedule_preempt_disable() which includes init/main.c and another location in mutex.c that sets the task state to TASK_RUNNING just before calling it.
But the one case where it can be something other than TASK_RUNNING, then we need to keep the current method.
OK, I think it is fine for the idle task to never enable preemption and I'll post a better change log patch.
Thanks!
-- Steve
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