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[RFC][PATCH 05/11] sched: Add preempt argument to __schedule()

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  [RFC][PATCH 05/11] sched: Add preempt argument to __schedule() Peter Zijlstra <peterz@infradead.org> - 2015-09-29 11:50 +0200
    Re: [RFC][PATCH 05/11] sched: Add preempt argument to __schedule() Frederic Weisbecker <fweisbec@gmail.com> - 2015-09-29 15:20 +0200
    Re: [RFC][PATCH 05/11] sched: Add preempt argument to __schedule() Steven Rostedt <rostedt@goodmis.org> - 2015-09-29 17:30 +0200
      Re: [RFC][PATCH 05/11] sched: Add preempt argument to __schedule() Steven Rostedt <rostedt@goodmis.org> - 2015-09-29 17:40 +0200
        Re: [RFC][PATCH 05/11] sched: Add preempt argument to __schedule() Peter Zijlstra <peterz@infradead.org> - 2015-09-29 17:40 +0200

#1234929 — [RFC][PATCH 05/11] sched: Add preempt argument to __schedule()

There is only a single PREEMPT_ACTIVE use in the regular __schedule()
path and that is to circumvent the task->state check. Since the code
setting PREEMPT_ACTIVE is the immediate caller of __schedule() we can
replace this with a function argument.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3045,7 +3045,7 @@ pick_next_task(struct rq *rq, struct tas
  *
  * WARNING: must be called with preemption disabled!
  */
-static void __sched __schedule(void)
+static void __sched __schedule(bool preempt)
 {
 	struct task_struct *prev, *next;
 	unsigned long *switch_count;
@@ -3085,7 +3085,7 @@ static void __sched __schedule(void)
 	rq->clock_skip_update <<= 1; /* promote REQ to ACT */
 
 	switch_count = &prev->nivcsw;
-	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
+	if (!preempt && prev->state) {
 		if (unlikely(signal_pending_state(prev->state, prev))) {
 			prev->state = TASK_RUNNING;
 		} else {
@@ -3150,7 +3150,7 @@ asmlinkage __visible void __sched schedu
 	sched_submit_work(tsk);
 	do {
 		preempt_disable();
-		__schedule();
+		__schedule(false);
 		sched_preempt_enable_no_resched();
 	} while (need_resched());
 }
@@ -3191,7 +3191,7 @@ static void __sched notrace preempt_sche
 {
 	do {
 		preempt_active_enter();
-		__schedule();
+		__schedule(true);
 		preempt_active_exit();
 
 		/*
@@ -3256,7 +3256,7 @@ asmlinkage __visible void __sched notrac
 		 * an infinite recursion.
 		 */
 		prev_ctx = exception_enter();
-		__schedule();
+		__schedule(true);
 		exception_exit(prev_ctx);
 
 		barrier();
@@ -3285,7 +3285,7 @@ asmlinkage __visible void __sched preemp
 	do {
 		preempt_active_enter();
 		local_irq_enable();
-		__schedule();
+		__schedule(true);
 		local_irq_disable();
 		preempt_active_exit();
 	} while (need_resched());


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#1235048

On Tue, Sep 29, 2015 at 11:28:30AM +0200, Peter Zijlstra wrote:
> There is only a single PREEMPT_ACTIVE use in the regular __schedule()
> path and that is to circumvent the task->state check. Since the code
> setting PREEMPT_ACTIVE is the immediate caller of __schedule() we can
> replace this with a function argument.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
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#1235244

On Tue, 29 Sep 2015 11:28:30 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> There is only a single PREEMPT_ACTIVE use in the regular __schedule()
> path and that is to circumvent the task->state check. Since the code
> setting PREEMPT_ACTIVE is the immediate caller of __schedule() we can
> replace this with a function argument.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---

Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve
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#1235300

On Tue, 29 Sep 2015 11:28:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 29 Sep 2015 11:28:30 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > There is only a single PREEMPT_ACTIVE use in the regular __schedule()
> > path and that is to circumvent the task->state check. Since the code
> > setting PREEMPT_ACTIVE is the immediate caller of __schedule() we can
> > replace this with a function argument.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> 
> Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

I just want to note that this scared me at first, because __schedule()
can be traced by the function tracer that can also do a
preempt_enable() which would schedule if preemption was enabled. But it
looks as __schedule() is always called with preemption disabled, thus,
no worries.

-- Steve

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#1235303

On Tue, Sep 29, 2015 at 11:30:26AM -0400, Steven Rostedt wrote:
> On Tue, 29 Sep 2015 11:28:39 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > On Tue, 29 Sep 2015 11:28:30 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > There is only a single PREEMPT_ACTIVE use in the regular __schedule()
> > > path and that is to circumvent the task->state check. Since the code
> > > setting PREEMPT_ACTIVE is the immediate caller of __schedule() we can
> > > replace this with a function argument.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > ---
> > 
> > Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
> 
> I just want to note that this scared me at first, because __schedule()
> can be traced by the function tracer that can also do a

See 11/11 :-)

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