[PATCH] schedule: SCHED_RR: Give a fresh time-slice to the task after after it suspends or relinquishes

[PATCH] schedule: SCHED_RR: Give a fresh time-slice to the task after after it suspends or relinquishes

[zhaoxiu.zeng]

Assuming the sched_rr_timeslice is 100ms, there are several tasks with the
same priority t1, t2, t3, ..., and t1 sleeps every 80ms, the scheduling
timing may be:
    t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
    80, 100, 100, ..., 20, 100, 100, ..., 60, 100, 100, ..., 40, 100, 100

After applying this patch, the scheduling timing may be:
    t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
    80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100


Signed-off-by: zhaoxiu.zeng <zhaoxiu.zeng@gmail.com>
---
 kernel/sched/rt.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index b48baaba2fc2..51798fefcb36 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1491,9 +1491,13 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
 {
 	struct sched_rt_entity *rt_se = &p->rt;
 
-	if (flags & ENQUEUE_WAKEUP)
+	if (flags & ENQUEUE_WAKEUP) {
 		rt_se->timeout = 0;
 
+		if (p->policy == SCHED_RR)
+			p->rt.time_slice = sched_rr_timeslice;
+	}
+
 	check_schedstat_required();
 	update_stats_wait_start_rt(rt_rq_of_se(rt_se), rt_se);
 
@@ -1544,7 +1548,12 @@ static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
 
 static void yield_task_rt(struct rq *rq)
 {
-	requeue_task_rt(rq, rq->curr, 0);
+	struct task_struct *p = rq->curr;
+
+	if (p->policy == SCHED_RR)
+		p->rt.time_slice = sched_rr_timeslice;
+
+	requeue_task_rt(rq, p, 0);
 }
 
 #ifdef CONFIG_SMP
-- 
2.32.0

Re: [PATCH] schedule: SCHED_RR: Give a fresh time-slice to the task after after it suspends or relinquishes

[Peter Zijlstra]

On Wed, Dec 22, 2021 at 05:15:26PM +0800, zhaoxiu.zeng wrote:
> Assuming the sched_rr_timeslice is 100ms, there are several tasks with the
> same priority t1, t2, t3, ..., and t1 sleeps every 80ms, the scheduling
> timing may be:
>     t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
>     80, 100, 100, ..., 20, 100, 100, ..., 60, 100, 100, ..., 40, 100, 100
> 
> After applying this patch, the scheduling timing may be:
>     t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
>     80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100
> 

Is this what POSIX mandates or why are you sending this to me ?

Re: [PATCH] schedule: SCHED_RR: Give a fresh time-slice to the task after after it suspends or relinquishes

[Zhaoxiu Zeng]

Peter Zijlstra <peterz@infradead.org> 于2021年12月22日周三 18:41写道：
>
> On Wed, Dec 22, 2021 at 05:15:26PM +0800, zhaoxiu.zeng wrote:
> > Assuming the sched_rr_timeslice is 100ms, there are several tasks with the
> > same priority t1, t2, t3, ..., and t1 sleeps every 80ms, the scheduling
> > timing may be:
> >     t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
> >     80, 100, 100, ..., 20, 100, 100, ..., 60, 100, 100, ..., 40, 100, 100
> >
> > After applying this patch, the scheduling timing may be:
> >     t1  t2   t3        t1  t2   t3        t1  t2   t3        t1  t2   t3
> >     80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100, ..., 80, 100, 100
> >
>
> Is this what POSIX mandates or why are you sending this to me ?

Thanks for your reply!

I don't see a definition of this in POSIX.
Give a fresh time-slice may decreases context switches, and be more
fairly to the tasks which suspended then resumed.

Re: [PATCH] schedule: SCHED_RR: Give a fresh time-slice to the task after after it suspends or relinquishes

[kernel test robot]

Hi "zhaoxiu.zeng",

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on v5.16-rc6 next-20211222]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/zhaoxiu-zeng/schedule-SCHED_RR-Give-a-fresh-time-slice-to-the-task-after-after-it-suspends-or-relinquishes/20211222-171838
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 82762d2af31a60081162890983a83499c9c7dd74
config: i386-randconfig-s001-20211222 (https://download.01.org/0day-ci/archive/20211223/202112230234.B6uAyy2x-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-dirty
        # https://github.com/0day-ci/linux/commit/7e5fd85c65d2efc13de4adaa5ebc522894f3d60c
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review zhaoxiu-zeng/schedule-SCHED_RR-Give-a-fresh-time-slice-to-the-task-after-after-it-suspends-or-relinquishes/20211222-171838
        git checkout 7e5fd85c65d2efc13de4adaa5ebc522894f3d60c
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash kernel/sched/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
   kernel/sched/rt.c:924:70: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/rt.c:924:70: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/rt.c:924:70: sparse:    struct task_struct *
   kernel/sched/rt.c:1010:38: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct task_struct *curr @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/rt.c:1010:38: sparse:     expected struct task_struct *curr
   kernel/sched/rt.c:1010:38: sparse:     got struct task_struct [noderef] __rcu *curr
>> kernel/sched/rt.c:1560:35: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct task_struct *p @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/rt.c:1560:35: sparse:     expected struct task_struct *p
   kernel/sched/rt.c:1560:35: sparse:     got struct task_struct [noderef] __rcu *curr
   kernel/sched/rt.c: note: in included file:
   kernel/sched/sched.h:2032:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct *
   kernel/sched/sched.h:2032:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct *
   kernel/sched/sched.h:2032:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2032:25: sparse:    struct task_struct *

vim +1560 kernel/sched/rt.c

  1557	
  1558	static void yield_task_rt(struct rq *rq)
  1559	{
> 1560		struct task_struct *p = rq->curr;
  1561	
  1562		if (p->policy == SCHED_RR)
  1563			p->rt.time_slice = sched_rr_timeslice;
  1564	
  1565		requeue_task_rt(rq, p, 0);
  1566	}
  1567	

---
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