[PATCH v3 04/20] cpumask: Introduce cpu_preferred_mask

[Shrikanth Hegde <sshegde@linux.ibm.com>]

This patch does
- Declare and Define cpu_preferred_mask.
- Get/Set helpers for it.

Values are set/clear by the scheduler by detecting the steal time values.

A CPU is set to preferred when it comes online. Later it may be
marked as non-preferred depending on steal time values with
steal monitor being enabled.

Always maintain design construct of preferred is subset of online.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 include/linux/cpumask.h | 21 ++++++++++++++++++++-
 kernel/cpu.c            | 16 ++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 80211900f373..025ad7778a6c 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -120,12 +120,20 @@ extern struct cpumask __cpu_enabled_mask;
 extern struct cpumask __cpu_present_mask;
 extern struct cpumask __cpu_active_mask;
 extern struct cpumask __cpu_dying_mask;
+
+#ifdef CONFIG_PREFERRED_CPU
+extern struct cpumask __cpu_preferred_mask;
+#else
+#define __cpu_preferred_mask __cpu_online_mask
+#endif
+
 #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
 #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
 #define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
 #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
 #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
 #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
+#define cpu_preferred_mask ((const struct cpumask *)&__cpu_preferred_mask)
 
 extern atomic_t __num_online_cpus;
 extern unsigned int __num_possible_cpus;
@@ -1164,6 +1172,7 @@ void init_cpu_possible(const struct cpumask *src);
 
 void set_cpu_online(unsigned int cpu, bool online);
 void set_cpu_possible(unsigned int cpu, bool possible);
+void set_cpu_preferred(unsigned int cpu, bool preferred);
 
 /**
  * to_cpumask - convert a NR_CPUS bitmap to a struct cpumask *
@@ -1256,7 +1265,12 @@ static __always_inline bool cpu_dying(unsigned int cpu)
 	return cpumask_test_cpu(cpu, cpu_dying_mask);
 }
 
-#else
+static __always_inline bool cpu_preferred(unsigned int cpu)
+{
+	return cpumask_test_cpu(cpu, cpu_preferred_mask);
+}
+
+#else	/* NR_CPUS <= 1 */
 
 #define num_online_cpus()	1U
 #define num_possible_cpus()	1U
@@ -1294,6 +1308,11 @@ static __always_inline bool cpu_dying(unsigned int cpu)
 	return false;
 }
 
+static __always_inline bool cpu_preferred(unsigned int cpu)
+{
+	return cpu == 0;
+}
+
 #endif /* NR_CPUS > 1 */
 
 #define cpu_is_offline(cpu)	unlikely(!cpu_online(cpu))
diff --git a/kernel/cpu.c b/kernel/cpu.c
index bc4f7a9ba64e..819167cb8bed 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3107,6 +3107,11 @@ EXPORT_SYMBOL(__cpu_dying_mask);
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
+#ifdef CONFIG_PREFERRED_CPU
+struct cpumask __cpu_preferred_mask __read_mostly;
+EXPORT_SYMBOL(__cpu_preferred_mask);
+#endif
+
 void init_cpu_present(const struct cpumask *src)
 {
 	cpumask_copy(&__cpu_present_mask, src);
@@ -3137,6 +3142,9 @@ void set_cpu_online(unsigned int cpu, bool online)
 		if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
 			atomic_dec(&__num_online_cpus);
 	}
+
+	/* preferred is always subset of online */
+	set_cpu_preferred(cpu, online);
 }
 
 /*
@@ -3154,6 +3162,14 @@ void set_cpu_possible(unsigned int cpu, bool possible)
 	}
 }
 
+void set_cpu_preferred(unsigned int cpu, bool preferred)
+{
+	if (!IS_ENABLED(CONFIG_PREFERRED_CPU))
+		return;
+
+	assign_cpu((cpu), &__cpu_preferred_mask, (preferred));
+}
+
 /*
  * Activate the first processor.
  */
-- 
2.47.3