[RFC PATCH] powerpc/mm: Use a non-idle variant of kick_all_cpus_sync

[Aneesh Kumar K.V]

What we really need is the ability to wait for other cpus to
finish local_irq_save/local_irq_restore region. We don't need to send
IPI to idle cpus in that case. Add a vairant of kick_all_cpus_sync
to do that. If idle_cpu_mask change during the call, we should be
ok because:
1) new cpus got added. In this case when they enter the critical path
   they would have seen the new values i modified before smp_wmb();

2) cpus got removed: In this case we are ok, because we send stray IPI
   to them

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
---
NOTE: 
This need closer review, because I am new to the area of cpu mask.

 arch/powerpc/mm/pgtable_64.c |  6 +++---
 include/linux/smp.h          |  9 +++++++++
 kernel/sched/fair.c          | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index 049d961802aa..e54b111f8737 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -590,7 +590,7 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
 	 * by sending an IPI to all the cpus and executing a dummy
 	 * function there.
 	 */
-	kick_all_cpus_sync();
+	poke_nonidle_cpus_sync();
 	/*
 	 * Now invalidate the hpte entries in the range
 	 * covered by pmd. This make sure we take a
@@ -670,7 +670,7 @@ void pmdp_splitting_flush(struct vm_area_struct *vma,
 	 * This ensures that generic code that rely on IRQ disabling
 	 * to prevent a parallel THP split work as expected.
 	 */
-	kick_all_cpus_sync();
+	poke_nonidle_cpus_sync();
 }
 
 /*
@@ -855,7 +855,7 @@ pmd_t pmdp_get_and_clear(struct mm_struct *mm,
 	 * different code paths. So make sure we wait for the parallel
 	 * find_linux_pte_or_hugepage to finish.
 	 */
-	kick_all_cpus_sync();
+	poke_nonidle_cpus_sync();
 	return old_pmd;
 }
 
diff --git a/include/linux/smp.h b/include/linux/smp.h
index c4414074bd88..16d539b94c31 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -101,6 +101,14 @@ int smp_call_function_any(const struct cpumask *mask,
 
 void kick_all_cpus_sync(void);
 void wake_up_all_idle_cpus(void);
+#ifdef CONFIG_NO_HZ_COMMON
+void poke_nonidle_cpus_sync(void);
+#else
+static inline void poke_nonidle_cpus_sync(void)
+{
+	return kick_all_cpus_sync();
+}
+#endif
 
 /*
  * Generic and arch helpers
@@ -150,6 +158,7 @@ smp_call_function_any(const struct cpumask *mask, smp_call_func_t func,
 
 static inline void kick_all_cpus_sync(void) {  }
 static inline void wake_up_all_idle_cpus(void) {  }
+static inline void poke_nonidle_cpus_sync(void) {  }
 
 #ifdef CONFIG_UP_LATE_INIT
 extern void __init up_late_init(void);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ffeaa4105e48..00abc6ae077b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7513,6 +7513,25 @@ static int sched_ilb_notifier(struct notifier_block *nfb,
 		return NOTIFY_DONE;
 	}
 }
+
+static void do_nothing(void *unused)
+{
+}
+
+void poke_nonidle_cpus_sync(void)
+{
+	struct cpumask mask;
+
+	/*
+	 * Make sure the change is visible before we poke the cpus
+	 */
+	smp_mb();
+	preempt_disable();
+	cpumask_andnot(&mask, cpu_online_mask, nohz.idle_cpus_mask);
+	smp_call_function_many(&mask, do_nothing, NULL, 1);
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(poke_nonidle_cpus_sync);
 #endif
 
 static DEFINE_SPINLOCK(balancing);
-- 
2.1.4