[PATCH] sched/core: fix formatting issues in sched_can_stop_tick()

[PATCH] sched/core: fix formatting issues in sched_can_stop_tick()

[Viresh Kumar]

sched_can_stop_tick() was using 7 spaces instead of 8 spaces or a 'tab' at the
beginning of each line. Which doesn't align with the Coding Guidelines.

Also it removes the *rq variable as it was used at only one place and hence we
can directly use this_rq() instead.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
I don't think rq = tihs_rq() has to be done before smp_mb(), in case yes sorry
for this patch :(

 kernel/sched/core.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 268a45e..13299c5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -666,18 +666,14 @@ static inline bool got_nohz_idle_kick(void)
 #ifdef CONFIG_NO_HZ_FULL
 bool sched_can_stop_tick(void)
 {
-       struct rq *rq;
-
-       rq = this_rq();
-
-       /* Make sure rq->nr_running update is visible after the IPI */
-       smp_rmb();
+	/* Make sure rq->nr_running update is visible after the IPI */
+	smp_rmb();
 
-       /* More than one running task need preemption */
-       if (rq->nr_running > 1)
-               return false;
+	/* More than one running task need preemption */
+	if (this_rq()->nr_running > 1)
+		return false;
 
-       return true;
+	return true;
 }
 #endif /* CONFIG_NO_HZ_FULL */
 
-- 
1.7.12.rc2.18.g61b472e

Re: [PATCH] sched/core: fix formatting issues in sched_can_stop_tick()

[Peter Zijlstra]

On Mon, Apr 14, 2014 at 09:47:41PM +0530, Viresh Kumar wrote:
> sched_can_stop_tick() was using 7 spaces instead of 8 spaces or a 'tab' at the
> beginning of each line. Which doesn't align with the Coding Guidelines.
> 
> Also it removes the *rq variable as it was used at only one place and hence we
> can directly use this_rq() instead.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> I don't think rq = tihs_rq() has to be done before smp_mb(), in case yes sorry
> for this patch :(
> 
>  kernel/sched/core.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 268a45e..13299c5 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -666,18 +666,14 @@ static inline bool got_nohz_idle_kick(void)
>  #ifdef CONFIG_NO_HZ_FULL
>  bool sched_can_stop_tick(void)
>  {
> +	/* Make sure rq->nr_running update is visible after the IPI */
> +	smp_rmb();
>  
> +	/* More than one running task need preemption */
> +	if (this_rq()->nr_running > 1)
> +		return false;
>  
> +	return true;
>  }
>  #endif /* CONFIG_NO_HZ_FULL */

AFAICT the smp_rmb() is entirely spurious, arch interrupts should ensure
consistency on their own. That is:

  CPU 0		  CPU 1

[w] X = 1
    IPI 1	    <int>
		[r] r = X

Should act as if there was a full memory barrier, making it so that the
read on CPU1 observes the write on CPU0.

Re: [PATCH] sched/core: fix formatting issues in sched_can_stop_tick()

[Frederic Weisbecker]

On Mon, Apr 14, 2014 at 08:38:38PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 14, 2014 at 09:47:41PM +0530, Viresh Kumar wrote:
> > sched_can_stop_tick() was using 7 spaces instead of 8 spaces or a 'tab' at the
> > beginning of each line. Which doesn't align with the Coding Guidelines.
> > 
> > Also it removes the *rq variable as it was used at only one place and hence we
> > can directly use this_rq() instead.
> > 
> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> > ---
> > I don't think rq = tihs_rq() has to be done before smp_mb(), in case yes sorry
> > for this patch :(
> > 
> >  kernel/sched/core.c | 16 ++++++----------
> >  1 file changed, 6 insertions(+), 10 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 268a45e..13299c5 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -666,18 +666,14 @@ static inline bool got_nohz_idle_kick(void)
> >  #ifdef CONFIG_NO_HZ_FULL
> >  bool sched_can_stop_tick(void)
> >  {
> > +	/* Make sure rq->nr_running update is visible after the IPI */
> > +	smp_rmb();
> >  
> > +	/* More than one running task need preemption */
> > +	if (this_rq()->nr_running > 1)
> > +		return false;
> >  
> > +	return true;
> >  }
> >  #endif /* CONFIG_NO_HZ_FULL */
> 
> AFAICT the smp_rmb() is entirely spurious, arch interrupts should ensure
> consistency on their own. That is:
> 
>   CPU 0		  CPU 1
> 
> [w] X = 1
>     IPI 1	    <int>
> 		[r] r = X
> 
> Should act as if there was a full memory barrier, making it so that the
> read on CPU1 observes the write on CPU0.

Right, I have a pending patch for that:
https://git.kernel.org/cgit/linux/kernel/git/frederic/linux-dynticks.git/commit/?h=nohz/ipi&id=ca981d9f87fe0f113ad972098cfe181180b3675a

Re: [PATCH] sched/core: fix formatting issues in sched_can_stop_tick()

[Viresh Kumar]

On 15 April 2014 04:18, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> Right, I have a pending patch for that:

> https://git.kernel.org/cgit/linux/kernel/git/frederic/linux-dynticks.git/commit/?h=nohz/ipi&id=ca981d9f87fe0f113ad972098cfe181180b3675a

Cool!! I will rebase my patch over yours and resend.