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Re: [PATCH] sched/numa: Restore sched feature NUMA to its earlier avatar.

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  Re: [PATCH] sched/numa: Restore sched feature NUMA to its earlier  avatar. Ingo Molnar <mingo@kernel.org> - 2015-07-09 10:10 +0200
    Re: [PATCH] sched/numa: Restore sched feature NUMA to its earlier  avatar. Srikar Dronamraju <srikar@linux.vnet.ibm.com> - 2015-07-10 19:30 +0200
      Re: [PATCH] sched/numa: Restore sched feature NUMA to its earlier  avatar. Ingo Molnar <mingo@kernel.org> - 2015-07-11 11:00 +0200

#1180509 — Re: [PATCH] sched/numa: Restore sched feature NUMA to its earlier avatar.

* Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> > So I find the patch, the description and the comments in the code conflicting and 
> > confusing.
> > 
> > The patch does this:
> > 
> > @@ -5676,10 +5676,10 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
> >         unsigned long src_faults, dst_faults;
> >         int src_nid, dst_nid;
> > 
> > -       if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
> > +       if (!sched_feat(NUMA) || !sched_feat(NUMA_FAVOUR_HIGHER))
> >                 return -1;
> > 
> > -       if (!sched_feat(NUMA))
> > +       if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
> >                 return -1;
> > 
> >         src_nid = cpu_to_node(env->src_cpu);
> > 
> > 
> > while the default for 'NUMA' is 0, 'NUMA_FAVOUR_HIGHER' is 1.
> > 
> > Which in itself is confusing: WTH do we have a generic switch called 'NUMA' and 
> > then have it disabled?
> 
> NUMA feature gets enabled on multi-node boxes because of
> 
> start_kernel() -> numa_policy_init() -> check_numabalancing_enable() ->
>  set_numabalancing_state() -> sched_feat_set("NUMA");

Ugh, that is nonsensical!

If CONFIG_SCHED_DEBUG is disabled then sched_features is a constant value:

  # define const_debug const

  ...

  extern const_debug unsigned int sysctl_sched_features;

sched_features are _only_ meant for debugging. They turn into an unchangeable set 
of features when SCHED_DEBUG is disabled - and that is very much by design.

The whole set_numabalancing_state() muck needs to be fixed.

Thanks,

	Ingo
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#1181781

> > > Which in itself is confusing: WTH do we have a generic switch called 'NUMA' and 
> > > then have it disabled?
> > 
> > NUMA feature gets enabled on multi-node boxes because of
> > 
> > start_kernel() -> numa_policy_init() -> check_numabalancing_enable() ->
> >  set_numabalancing_state() -> sched_feat_set("NUMA");
> 
> Ugh, that is nonsensical!
> 
> If CONFIG_SCHED_DEBUG is disabled then sched_features is a constant value:
> 
>   # define const_debug const
> 
>   ...
> 
>   extern const_debug unsigned int sysctl_sched_features;
> 
> sched_features are _only_ meant for debugging. They turn into an unchangeable set 
> of features when SCHED_DEBUG is disabled - and that is very much by design.
> 
> The whole set_numabalancing_state() muck needs to be fixed.

Would something like the below suffice. If yes I can send out a formal
patch for the same. Here we are moving numabalancing_enabled variable to
common i.e for both CONFIG_SCHED_DEBUG and !CONFIG_SCHED_DEBUG.

Also removing sched_feat_numa because its no more getting used.
numabalancing_enabled is already being used similarly in task_tick_fair
and task_numa_fault.

-------------->8------------------------------------------------------8<--------------

 kernel/sched/core.c  | 5 +++--
 kernel/sched/fair.c  | 2 +-
 kernel/sched/sched.h | 6 ------
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b4bad10..69ccbda4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2059,17 +2059,18 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 }
 
 #ifdef CONFIG_NUMA_BALANCING
+__read_mostly bool numabalancing_enabled;
+
 #ifdef CONFIG_SCHED_DEBUG
 void set_numabalancing_state(bool enabled)
 {
+	numabalancing_enabled = enabled;
 	if (enabled)
 		sched_feat_set("NUMA");
 	else
 		sched_feat_set("NO_NUMA");
 }
 #else
-__read_mostly bool numabalancing_enabled;
-
 void set_numabalancing_state(bool enabled)
 {
 	numabalancing_enabled = enabled;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 587a2f6..1b86455 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5679,7 +5679,7 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
 		return -1;
 
-	if (!sched_feat(NUMA))
+	if (!numabalancing_enabled)
 		return -1;
 
 	src_nid = cpu_to_node(env->src_cpu);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 84d4879..d460fe3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1014,14 +1014,8 @@ extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
 #endif /* SCHED_DEBUG && HAVE_JUMP_LABEL */
 
 #ifdef CONFIG_NUMA_BALANCING
-#define sched_feat_numa(x) sched_feat(x)
-#ifdef CONFIG_SCHED_DEBUG
-#define numabalancing_enabled sched_feat_numa(NUMA)
-#else
 extern bool numabalancing_enabled;
-#endif /* CONFIG_SCHED_DEBUG */
 #else
-#define sched_feat_numa(x) (0)
 #define numabalancing_enabled (0)
 #endif /* CONFIG_NUMA_BALANCING */
 


-- 
Thanks and Regards
Srikar Dronamraju

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#1182113

* Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> > > > Which in itself is confusing: WTH do we have a generic switch called 'NUMA' and 
> > > > then have it disabled?
> > > 
> > > NUMA feature gets enabled on multi-node boxes because of
> > > 
> > > start_kernel() -> numa_policy_init() -> check_numabalancing_enable() ->
> > >  set_numabalancing_state() -> sched_feat_set("NUMA");
> > 
> > Ugh, that is nonsensical!
> > 
> > If CONFIG_SCHED_DEBUG is disabled then sched_features is a constant value:
> > 
> >   # define const_debug const
> > 
> >   ...
> > 
> >   extern const_debug unsigned int sysctl_sched_features;
> > 
> > sched_features are _only_ meant for debugging. They turn into an unchangeable set 
> > of features when SCHED_DEBUG is disabled - and that is very much by design.
> > 
> > The whole set_numabalancing_state() muck needs to be fixed.
> 
> Would something like the below suffice. If yes I can send out a formal
> patch for the same. Here we are moving numabalancing_enabled variable to
> common i.e for both CONFIG_SCHED_DEBUG and !CONFIG_SCHED_DEBUG.
> 
> Also removing sched_feat_numa because its no more getting used.
> numabalancing_enabled is already being used similarly in task_tick_fair
> and task_numa_fault.
> 
> -------------->8------------------------------------------------------8<--------------
> 
>  kernel/sched/core.c  | 5 +++--
>  kernel/sched/fair.c  | 2 +-
>  kernel/sched/sched.h | 6 ------
>  3 files changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78b4bad10..69ccbda4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2059,17 +2059,18 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  }
>  
>  #ifdef CONFIG_NUMA_BALANCING
> +__read_mostly bool numabalancing_enabled;

s/numabalancing_enabled/sched_numa_balancing

Other than that this would be OK.

Thanks,

	Ingo
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