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 <[email protected]>
---
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
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 <[email protected]>
> ---
> 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.
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 <[email protected]>
> > ---
> > 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
On 15 April 2014 04:18, Frederic Weisbecker <[email protected]> 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.