Messages in this thread Patch in this message | | | From | JaeJoon Jung <> | Date | Mon, 13 Feb 2023 10:11:04 +0900 | Subject | [kernel/sched/core.c] Review and Modified of the prio_less() about sched class priority. |
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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.
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