linux-kernel - Re: [PATCH] kernel/sched/core.c: Modified prio

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Message-ID: <CAHOvCC544e8fuEvP6bSm7j0C5SQu6nd+StMcUhh_+aWBcPhNAQ@mail.gmail.com>
Date:   Wed, 22 Feb 2023 09:51:51 +0900
From:   JaeJoon Jung <rgbi3307@...il.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/sched/core.c: Modified prio_less().

I'm sorry for the inconvenience caused by my carelessness.
I had the problem you pointed out by copying and sending the contents
generated by git patch as text.
I will learn the git-send-email method you shared and send it again.

Thanks.

On Tue, 21 Feb 2023 at 22:17, Bagas Sanjaya <bagasdotme@...il.com> wrote:
>
> On Tue, Feb 21, 2023 at 05:24:27PM +0900, JaeJoon Jung wrote:
> > 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.
> > In the prio_less() function in kernel/sched/core.c,
> > the less value can be determined by pointer operation as follows.
> >
> > If the prio_less() function is modified as follows,
> > the __task_prio() function is not required.
>
> By what?
>
> >
> > Thanks,
> >
> >
> > Signed-off-by: JaeJoon Jung <rgbi3307@...il.com>
> > ---
> >  kernel/sched/core.c | 42 +++++++++++-------------------------------
> >  1 file changed, 11 insertions(+), 31 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 2a4918a1faa9..75075d92a198 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 +161,17 @@ 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 pa = __task_prio(a), pb = __task_prio(b);
> > -
> > - 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;
> > +        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;
> >  }
>
> I smell indentation-corrupted patch here. Please use git-send-email(1)
> to submit patches.
>
> For the patch subject, I can't imagine what are you doing since you
> wrote too generic subject ("Modified foo") without clearly describe in
> the patch description what are you doing. How can maintainers accept
> your patch if you don't take care of how to describe it?
>
> Last but not least, don't top-post when replying; reply inline with
> appropriate context instead.
>
> Thanks.
>
> --
> An old man doll... just what I always wanted! - Clara