[PATCH 11/32] cpuset: Set up interface for nohz flag

[Frederic Weisbecker]

Prepare the interface to implement the nohz cpuset flag.
This flag, once set, will tell the system to try to
shutdown the periodic timer tick when possible.

We use here a per cpu refcounter. As long as a CPU
is contained into at least one cpuset that has the
nohz flag set, it is part of the set of CPUs that
run into adaptive nohz mode.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tim Pepper <lnxninja@xxxxxxxxxxxxxxxxxx>
---
 arch/Kconfig           |    3 ++
 include/linux/cpuset.h |   22 ++++++++++++++++++++
 init/Kconfig           |    8 +++++++
 kernel/cpuset.c        |   52 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 85 insertions(+), 0 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 341ac95..5fe21c4 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -172,6 +172,9 @@ config HAVE_ARCH_JUMP_LABEL
 	bool
 
 config HAVE_ARCH_MUTEX_CPU_RELAX
+       bool
+
+config HAVE_CPUSETS_NO_HZ
 	bool
 
 config HAVE_RCU_TABLE_FREE
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index e9eaec5..62e5d5a 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -244,4 +244,26 @@ static inline void put_mems_allowed(void)
 
 #endif /* !CONFIG_CPUSETS */
 
+#ifdef CONFIG_CPUSETS_NO_HZ
+
+DECLARE_PER_CPU(int, cpu_adaptive_nohz_ref);
+
+static inline bool cpuset_cpu_adaptive_nohz(int cpu)
+{
+	if (per_cpu(cpu_adaptive_nohz_ref, cpu) > 0)
+		return true;
+
+	return false;
+}
+
+static inline bool cpuset_adaptive_nohz(void)
+{
+	if (__get_cpu_var(cpu_adaptive_nohz_ref) > 0)
+		return true;
+
+	return false;
+}
+
+#endif /* CONFIG_CPUSETS_NO_HZ */
+
 #endif /* _LINUX_CPUSET_H */
diff --git a/init/Kconfig b/init/Kconfig
index 3cf7855..0cb591a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -624,6 +624,14 @@ config PROC_PID_CPUSET
 	depends on CPUSETS
 	default y
 
+config CPUSETS_NO_HZ
+       bool "Tickless cpusets"
+       depends on CPUSETS && HAVE_CPUSETS_NO_HZ
+       help
+         This options let you apply a nohz property to a cpuset such
+	 that the periodic timer tick tries to be avoided when possible on
+	 the concerned CPUs.
+
 config CGROUP_CPUACCT
 	bool "Simple CPU accounting cgroup subsystem"
 	help
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9c9b754..3135096 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -132,6 +132,7 @@ typedef enum {
 	CS_SCHED_LOAD_BALANCE,
 	CS_SPREAD_PAGE,
 	CS_SPREAD_SLAB,
+	CS_ADAPTIVE_NOHZ,
 } cpuset_flagbits_t;
 
 /* convenient tests for these bits */
@@ -170,6 +171,11 @@ static inline int is_spread_slab(const struct cpuset *cs)
 	return test_bit(CS_SPREAD_SLAB, &cs->flags);
 }
 
+static inline int is_adaptive_nohz(const struct cpuset *cs)
+{
+	return test_bit(CS_ADAPTIVE_NOHZ, &cs->flags);
+}
+
 static struct cpuset top_cpuset = {
 	.flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
 };
@@ -1189,6 +1195,31 @@ static void cpuset_change_flag(struct task_struct *tsk,
 	cpuset_update_task_spread_flag(cgroup_cs(scan->cg), tsk);
 }
 
+#ifdef CONFIG_CPUSETS_NO_HZ
+
+DEFINE_PER_CPU(int, cpu_adaptive_nohz_ref);
+
+static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
+{
+	int cpu;
+	int val;
+
+	if (is_adaptive_nohz(old_cs) == is_adaptive_nohz(cs))
+		return;
+
+	for_each_cpu(cpu, cs->cpus_allowed) {
+		if (is_adaptive_nohz(cs))
+			per_cpu(cpu_adaptive_nohz_ref, cpu) += 1;
+		else
+			per_cpu(cpu_adaptive_nohz_ref, cpu) -= 1;
+	}
+}
+#else
+static inline void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
+{
+}
+#endif
+
 /*
  * update_tasks_flags - update the spread flags of tasks in the cpuset.
  * @cs: the cpuset in which each task's spread flags needs to be changed
@@ -1254,6 +1285,8 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
 	spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
 			|| (is_spread_page(cs) != is_spread_page(trialcs)));
 
+	update_nohz_cpus(cs, trialcs);
+
 	mutex_lock(&callback_mutex);
 	cs->flags = trialcs->flags;
 	mutex_unlock(&callback_mutex);
@@ -1472,6 +1505,7 @@ typedef enum {
 	FILE_MEMORY_PRESSURE,
 	FILE_SPREAD_PAGE,
 	FILE_SPREAD_SLAB,
+	FILE_ADAPTIVE_NOHZ,
 } cpuset_filetype_t;
 
 static int cpuset_write_u64(struct cgroup *cgrp, struct cftype *cft, u64 val)
@@ -1511,6 +1545,11 @@ static int cpuset_write_u64(struct cgroup *cgrp, struct cftype *cft, u64 val)
 	case FILE_SPREAD_SLAB:
 		retval = update_flag(CS_SPREAD_SLAB, cs, val);
 		break;
+#ifdef CONFIG_CPUSETS_NO_HZ
+	case FILE_ADAPTIVE_NOHZ:
+		retval = update_flag(CS_ADAPTIVE_NOHZ, cs, val);
+		break;
+#endif
 	default:
 		retval = -EINVAL;
 		break;
@@ -1670,6 +1709,10 @@ static u64 cpuset_read_u64(struct cgroup *cont, struct cftype *cft)
 		return is_spread_page(cs);
 	case FILE_SPREAD_SLAB:
 		return is_spread_slab(cs);
+#ifdef CONFIG_CPUSETS_NO_HZ
+	case FILE_ADAPTIVE_NOHZ:
+		return is_adaptive_nohz(cs);
+#endif
 	default:
 		BUG();
 	}
@@ -1778,6 +1821,15 @@ static struct cftype files[] = {
 		.write_u64 = cpuset_write_u64,
 		.private = FILE_SPREAD_SLAB,
 	},
+
+#ifdef CONFIG_CPUSETS_NO_HZ
+	{
+		.name = "adaptive_nohz",
+		.read_u64 = cpuset_read_u64,
+		.write_u64 = cpuset_write_u64,
+		.private = FILE_ADAPTIVE_NOHZ,
+	},
+#endif
 };
 
 static struct cftype cft_memory_pressure_enabled = {
-- 
1.7.5.4

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