Re: [PATCH v2] sched/features: Fix !CONFIG_JUMP_LABEL case

From: Patrick Bellasi <patrick.bellasi@matbug.net>
To: Juri Lelli <juri.lelli@redhat.com>
Cc: peterz@infradead.org, mingo@redhat.com,
	linux-kernel@vger.kernel.org, bristot@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	chris.redpath@arm.com, rostedt@goodmis.org, bsegall@google.com,
	mgorman@suse.de, valentin.schneider@arm.com
Subject: Re: [PATCH v2] sched/features: Fix !CONFIG_JUMP_LABEL case
Date: Tue, 13 Oct 2020 10:26:59 +0200	[thread overview]
Message-ID: <878scail9o.derkling@matbug.net> (raw)
In-Reply-To: <20201013053114.160628-1-juri.lelli@redhat.com>

On Tue, Oct 13, 2020 at 07:31:14 +0200, Juri Lelli <juri.lelli@redhat.com> wrote...

> Commit 765cc3a4b224e ("sched/core: Optimize sched_feat() for
> !CONFIG_SCHED_DEBUG builds") made sched features static for
> !CONFIG_SCHED_DEBUG configurations, but overlooked the CONFIG_
> SCHED_DEBUG enabled and !CONFIG_JUMP_LABEL cases. For the latter echoing
> changes to /sys/kernel/debug/sched_features has the nasty effect of
> effectively changing what sched_features reports, but without actually
> changing the scheduler behaviour (since different translation units get
> different sysctl_sched_features).

Hops, yes, I think I missed to properly check that config :/
Good spot!

> Fix CONFIG_SCHED_DEBUG and !CONFIG_JUMP_LABEL configurations by properly
> restructuring ifdefs.
>
> Fixes: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds")
> Co-developed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>

(did you get some wrong formatting for the changelog above?)

> ---
> v1->v2
>  - use CONFIG_JUMP_LABEL (and not the old HAVE_JUMP_LABEL) [Valentin]
> ---
>  kernel/sched/core.c  |  2 +-
>  kernel/sched/sched.h | 13 ++++++++++---
>  2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3dc415f58bd7..a7949e3ed7e7 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -44,7 +44,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp);
>  
>  DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
>  
> -#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_JUMP_LABEL)
> +#ifdef CONFIG_SCHED_DEBUG
>  /*
>   * Debugging: various feature bits
>   *
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 28709f6b0975..8d1ca65db3b0 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1629,7 +1629,7 @@ enum {
>  
>  #undef SCHED_FEAT
>  
> -#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_JUMP_LABEL)
> +#ifdef CONFIG_SCHED_DEBUG
>  
>  /*
>   * To support run-time toggling of sched features, all the translation units
> @@ -1637,6 +1637,7 @@ enum {
>   */
>  extern const_debug unsigned int sysctl_sched_features;
>  
> +#ifdef CONFIG_JUMP_LABEL
>  #define SCHED_FEAT(name, enabled)					\
>  static __always_inline bool static_branch_##name(struct static_key *key) \
>  {									\
> @@ -1649,7 +1650,13 @@ static __always_inline bool static_branch_##name(struct static_key *key) \
>  extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
>  #define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
>  
> -#else /* !(SCHED_DEBUG && CONFIG_JUMP_LABEL) */
> +#else /* !CONFIG_JUMP_LABEL */
> +
> +#define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
> +
> +#endif /* CONFIG_JUMP_LABEL */
> +
> +#else /* !SCHED_DEBUG */
>  
>  /*
>   * Each translation unit has its own copy of sysctl_sched_features to allow
> @@ -1665,7 +1672,7 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
>  
>  #define sched_feat(x) !!(sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
>  
> -#endif /* SCHED_DEBUG && CONFIG_JUMP_LABEL */
> +#endif /* SCHED_DEBUG */
>  
>  extern struct static_key_false sched_numa_balancing;
>  extern struct static_key_false sched_schedstats;