* [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority.
@ 2023-02-13 1:11 JaeJoon Jung
2023-02-13 10:08 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: JaeJoon Jung @ 2023-02-13 1:11 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar; +Cc: linux-kernel
The sched_class structure is defined to be sorted by pointer size.
You can see it in the macro definition like this:
kernel/sched/sched.h
#define DEFINE_SCHED_CLASS(name)
const struct sched_class name##_sched_class \
__aligned(__alignof__(struct sched_class)) \
__section("__" #name "_sched_class")
include/asm-generic/vmlinux.lds.h
#define SCHED_DATA \
STRUCT_ALIGN(); \
__sched_class_highest = .; \
*(__stop_sched_class) \
*(__dl_sched_class) \
*(__rt_sched_class) \
*(__fair_sched_class) \
*(__idle_sched_class) \
__sched_class_lowest = .;
And in the System.map file,
you can see that they are arranged in memory address order.
System.map
----------------------------------------------------------------
ffffffff8260d520 R __sched_class_highest
ffffffff8260d520 R stop_sched_class
ffffffff8260d5f0 R dl_sched_class
ffffffff8260d6c0 R rt_sched_class
ffffffff8260d790 R fair_sched_class
ffffffff8260d860 R idle_sched_class
ffffffff8260d930 R __sched_class_lowest
----------------------------------------------------------------
This matches the sched class priority.
Therefore, in the prio_less() function in kernel/sched/core.c,
the less value can be determined by pointer operation as follows.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f730b6fe94a7..7a64ac8ea3d8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -151,21 +151,6 @@ __read_mostly int scheduler_running;
DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
-/* kernel prio, less is more */
-static inline int __task_prio(struct task_struct *p)
-{
- if (p->sched_class == &stop_sched_class) /* trumps deadline */
- return -2;
-
- if (rt_prio(p->prio)) /* includes deadline */
- return p->prio; /* [-1, 99] */
-
- if (p->sched_class == &idle_sched_class)
- return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
-
- return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
-}
-
/*
* l(a,b)
* le(a,b) := !l(b,a)
@@ -176,22 +161,18 @@ static inline int __task_prio(struct task_struct *p)
/* real prio, less is less */
static inline bool prio_less(struct task_struct *a, struct
task_struct *b, bool in_fi)
{
+ int less = a->sched_class - b->sched_class;
- int pa = __task_prio(a), pb = __task_prio(b);
+ if (less == 0) {
+ if (a->sched_class == &dl_sched_class)
+ return !dl_time_before(a->dl.deadline, b->dl.deadline);
- if (-pa < -pb)
- return true;
-
- if (-pb < -pa)
- return false;
-
- if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
- return !dl_time_before(a->dl.deadline, b->dl.deadline);
-
- if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
- return cfs_prio_less(a, b, in_fi);
-
- return false;
+ else if (a->sched_class == &fair_sched_class)
+ return cfs_prio_less(a, b, in_fi);
+ else
+ return false;
+ } else
+ return (less > 0) ? true : false;
}
If the prio_less() function is modified as above, the __task_prio()
function is not required.
Please review.
Thanks,
From JaeJoon Jung.
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority.
2023-02-13 1:11 [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority JaeJoon Jung
@ 2023-02-13 10:08 ` Peter Zijlstra
2023-02-13 23:44 ` JaeJoon Jung
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2023-02-13 10:08 UTC (permalink / raw)
To: JaeJoon Jung; +Cc: Ingo Molnar, linux-kernel
On Mon, Feb 13, 2023 at 10:11:04AM +0900, JaeJoon Jung wrote:
> The sched_class structure is defined to be sorted by pointer size.
> @@ -176,22 +161,18 @@ static inline int __task_prio(struct task_struct *p)
> /* real prio, less is less */
> static inline bool prio_less(struct task_struct *a, struct
> task_struct *b, bool in_fi)
> {
> + int less = a->sched_class - b->sched_class;
>
> + if (less == 0) {
> + if (a->sched_class == &dl_sched_class)
> + return !dl_time_before(a->dl.deadline, b->dl.deadline);
>
> + else if (a->sched_class == &fair_sched_class)
> + return cfs_prio_less(a, b, in_fi);
> + else
> + return false;
> + } else
> + return (less > 0) ? true : false;
> }
>
> If the prio_less() function is modified as above, the __task_prio()
> function is not required.
Yeah, except your patch is whitespace mangled..
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority.
2023-02-13 10:08 ` Peter Zijlstra
@ 2023-02-13 23:44 ` JaeJoon Jung
0 siblings, 0 replies; 3+ messages in thread
From: JaeJoon Jung @ 2023-02-13 23:44 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: Ingo Molnar, linux-kernel
Thank you for answering.
Is it going to be reflected in your patch?
JaeJoon Jung.
On Mon, 13 Feb 2023 at 19:08, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Feb 13, 2023 at 10:11:04AM +0900, JaeJoon Jung wrote:
> > The sched_class structure is defined to be sorted by pointer size.
> > @@ -176,22 +161,18 @@ static inline int __task_prio(struct task_struct *p)
> > /* real prio, less is less */
> > static inline bool prio_less(struct task_struct *a, struct
> > task_struct *b, bool in_fi)
> > {
> > + int less = a->sched_class - b->sched_class;
> >
> > + if (less == 0) {
> > + if (a->sched_class == &dl_sched_class)
> > + return !dl_time_before(a->dl.deadline, b->dl.deadline);
> >
> > + else if (a->sched_class == &fair_sched_class)
> > + return cfs_prio_less(a, b, in_fi);
> > + else
> > + return false;
> > + } else
> > + return (less > 0) ? true : false;
> > }
> >
> > If the prio_less() function is modified as above, the __task_prio()
> > function is not required.
>
> Yeah, except your patch is whitespace mangled..
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-02-13 1:11 [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority JaeJoon Jung
2023-02-13 10:08 ` Peter Zijlstra
2023-02-13 23:44 ` JaeJoon Jung
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