!877 sched: fix performance degradation on lmbench

Merge Pull Request from: @barry19901226 
 
There are worse performance with the 'Fixes'
when running "./lat_ctx -P $SYNC_MAX -s 64 16".

The 'Fixes' which allocates memory for p->prefer_cpus
even if "prefer_cpus" not be set.

Before the 'Fixes', only test "p->prefer_cpus",
after, add test "!cpumask_empty(p->prefer_cpus)"
which causing performance degradation.

select_task_rq_fair
  ->set_task_select_cpus
    ->prefer_cpus_valid  ----  test cpumask_empty(p->prefer_cpus) 
 
Link:https://gitee.com/openeuler/kernel/pulls/877 

Reviewed-by: Zucheng Zheng <zhengzucheng@huawei.com> 
Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com> 

fs/proc/base.c

@@ -3298,6 +3298,12 @@ static ssize_t preferred_cpuset_write(struct file *file, const char __user *buf,
 	if (retval < 0)
 		goto out_free_cpumask;
 
+	if (!cpumask_empty(new_mask)) {
+		cpus_read_lock();
+		dynamic_affinity_enable();
+		cpus_read_unlock();
+	}
+
 	retval = count;
 
 out_free_cpumask:

include/linux/sched.h

@@ -2227,6 +2227,7 @@ int set_prefer_cpus_ptr(struct task_struct *p,
 			const struct cpumask *new_mask);
 int sched_prefer_cpus_fork(struct task_struct *p, struct cpumask *mask);
 void sched_prefer_cpus_free(struct task_struct *p);
+void dynamic_affinity_enable(void);
 #endif
 
 #ifdef CONFIG_BPF_SCHED

kernel/cgroup/cpuset.c

@@ -734,6 +734,9 @@ static int update_prefer_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 
 	update_tasks_prefer_cpumask(trialcs);
 
+	if (!cpumask_empty(trialcs->prefer_cpus))
+		dynamic_affinity_enable();
+
 	spin_lock_irq(&callback_lock);
 	cpumask_copy(cs->prefer_cpus, trialcs->prefer_cpus);
 	spin_unlock_irq(&callback_lock);

kernel/sched/fair.c

@@ -7067,6 +7067,27 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 }
 
 #ifdef CONFIG_QOS_SCHED_DYNAMIC_AFFINITY
+
+#ifdef CONFIG_JUMP_LABEL
+static DEFINE_STATIC_KEY_FALSE(__dynamic_affinity_used);
+
+static inline bool dynamic_affinity_used(void)
+{
+	return static_branch_unlikely(&__dynamic_affinity_used);
+}
+
+void dynamic_affinity_enable(void)
+{
+	static_branch_enable_cpuslocked(&__dynamic_affinity_used);
+}
+
+#else /* CONFIG_JUMP_LABEL */
+static bool dynamic_affinity_used(void)
+{
+	return true;
+}
+#endif
+
 /*
  * Low utilization threshold for CPU
  *
@@ -7076,6 +7097,9 @@ int sysctl_sched_util_low_pct = 85;
 
 static inline bool prefer_cpus_valid(struct task_struct *p)
 {
+	if (!dynamic_affinity_used())
+		return false;
+
 	return p->prefer_cpus &&
 	       !cpumask_empty(p->prefer_cpus) &&
 	       !cpumask_equal(p->prefer_cpus, p->cpus_ptr) &&