linux-kernel - Re: [PATCH v2 2/3] sched: make migrate_enable/migrate

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Message-ID: <CADxym3Z7xtda+sf1PL8i_1TY8tqy-e3GqM1vAVJu5_VZ+CazMg@mail.gmail.com>
Date: Wed, 20 Aug 2025 10:32:56 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com, ast@...nel.org, daniel@...earbox.net, 
	john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev, 
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, 
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, 
	simona.vetter@...ll.ch, tzimmermann@...e.de, jani.nikula@...el.com, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v2 2/3] sched: make migrate_enable/migrate_disable inline

On Tue, Aug 19, 2025 at 8:32 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Aug 19, 2025 at 09:58:31AM +0800, Menglong Dong wrote:
>
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index be00629f0ba4..00383fed9f63 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -119,6 +119,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
> >  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_compute_energy_tp);
> >
> >  DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> > +EXPORT_SYMBOL_GPL(runqueues);
>
> Oh no, absolutely not.
>
> You never, ever, export a variable, and certainly not this one.
>
> How about something like so?
>
> I tried 'clever' things with export inline, but the compiler hates me,
> so the below is the best I could make work.

I see. You mean that we don't export the various, and use the
inlined version in vmlinux, and use the external version in modules,
which I think is nice ;)

(I were not aware that we should export various :/)

I'll try your advice.

Thanks!
Menglong Dong

>
> ---
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2315,6 +2315,7 @@ static __always_inline void alloc_tag_re
>  #define alloc_tag_restore(_tag, _old)          do {} while (0)
>  #endif
>
> +#ifndef MODULE
>  #ifndef COMPILE_OFFSETS
>
>  extern void __migrate_enable(void);
> @@ -2328,7 +2329,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq
>  #define this_rq_raw() PERCPU_PTR(&runqueues)
>  #endif
>
> -static inline void migrate_enable(void)
> +static inline void _migrate_enable(void)
>  {
>         struct task_struct *p = current;
>
> @@ -2363,7 +2364,7 @@ static inline void migrate_enable(void)
>         (*(unsigned int *)((void *)this_rq_raw() + RQ_nr_pinned))--;
>  }
>
> -static inline void migrate_disable(void)
> +static inline void _migrate_disable(void)
>  {
>         struct task_struct *p = current;
>
> @@ -2382,10 +2383,30 @@ static inline void migrate_disable(void)
>         (*(unsigned int *)((void *)this_rq_raw() + RQ_nr_pinned))++;
>         p->migration_disabled = 1;
>  }
> -#else
> -static inline void migrate_disable(void) { }
> -static inline void migrate_enable(void) { }
> -#endif
> +#else /* !COMPILE_OFFSETS */
> +static inline void _migrate_disable(void) { }
> +static inline void _migrate_enable(void) { }
> +#endif /* !COMPILE_OFFSETS */
> +
> +#ifndef CREATE_MIGRATE_DISABLE
> +static inline void migrate_disable(void)
> +{
> +       _migrate_disable();
> +}
> +
> +static inline void migrate_enable(void)
> +{
> +       _migrate_enable();
> +}
> +#else /* CREATE_MIGRATE_DISABLE */
> +extern void migrate_disable(void);
> +extern void migrate_enable(void);
> +#endif /* CREATE_MIGRATE_DISABLE */
> +
> +#else /* !MODULE */
> +extern void migrate_disable(void);
> +extern void migrate_enable(void);
> +#endif /* !MODULE */
>
>  DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable())
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7,6 +7,9 @@
>   *  Copyright (C) 1991-2002  Linus Torvalds
>   *  Copyright (C) 1998-2024  Ingo Molnar, Red Hat
>   */
> +#define CREATE_MIGRATE_DISABLE
> +#include <linux/sched.h>
> +
>  #include <linux/highmem.h>
>  #include <linux/hrtimer_api.h>
>  #include <linux/ktime_api.h>
> @@ -119,7 +122,6 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_updat
>  EXPORT_TRACEPOINT_SYMBOL_GPL(sched_compute_energy_tp);
>
>  DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
> -EXPORT_SYMBOL_GPL(runqueues);
>
>  #ifdef CONFIG_SCHED_PROXY_EXEC
>  DEFINE_STATIC_KEY_TRUE(__sched_proxy_exec);
> @@ -2382,6 +2384,11 @@ static void migrate_disable_switch(struc
>         __do_set_cpus_allowed(p, &ac);
>  }
>
> +void migrate_disable(void)
> +{
> +       _migrate_disable();
> +}
> +
>  void __migrate_enable(void)
>  {
>         struct task_struct *p = current;
> @@ -2392,7 +2399,11 @@ void __migrate_enable(void)
>
>         __set_cpus_allowed_ptr(p, &ac);
>  }
> -EXPORT_SYMBOL_GPL(__migrate_enable);
> +
> +void migrate_enable(void)
> +{
> +       _migrate_enable();
> +}
>
>  static inline bool rq_has_pinned_tasks(struct rq *rq)
>  {