nohz: Remove nohz_cpu_mask

RCU no longer uses this global variable, nor does anyone else.  This
commit therefore removes this variable.  This reduces memory footprint
and also removes some atomic instructions and memory barriers from
the dyntick-idle path.

Signed-off-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4ac2c0578e0ff9133c4c761fcf3291879ae646d4..6ee91e20353bcc9a7239215beb7884505b29bd3b 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -270,7 +270,6 @@ extern void init_idle_bootup_task(struct task_struct *idle);
 
 extern int runqueue_is_locked(int cpu);
 
-extern cpumask_var_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
 extern void select_nohz_load_balancer(int stop_tick);
 extern int get_nohz_timer_target(void);

diff --git a/kernel/sched.c b/kernel/sched.c
index e24cebe0e6cb45d1f2a88da778282cd129664b5e..3e552563045909ba881e1fb19d004619f8f88a27 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5979,15 +5979,6 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
        ftrace_graph_init_idle_task(idle, cpu);
 }
 
-/*
- * In a system that switches off the HZ timer nohz_cpu_mask
- * indicates which cpus entered this state. This is used
- * in the rcu update to wait only for active cpus. For system
- * which do not switch off the HZ timer nohz_cpu_mask should
- * always be CPU_BITS_NONE.
- */
-cpumask_var_t nohz_cpu_mask;
-
 /*
  * Increase the granularity value when there are more CPUs,
  * because with more CPUs the 'effective latency' as visible
@@ -8200,8 +8191,6 @@ void __init sched_init(void)
         */
        current->sched_class = &fair_sched_class;
 
-       /* Allocate the nohz_cpu_mask if CONFIG_CPUMASK_OFFSTACK */
-       zalloc_cpumask_var(&nohz_cpu_mask, GFP_NOWAIT);
 #ifdef CONFIG_SMP
        zalloc_cpumask_var(&sched_domains_tmpmask, GFP_NOWAIT);
 #ifdef CONFIG_NO_HZ

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index d5097c44b407e25a1acae0f5d85c520eda555ae5..eb98e55196b96275f6ee73af0b5d6e351d9162dc 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -139,7 +139,6 @@ static void tick_nohz_update_jiffies(ktime_t now)
        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
        unsigned long flags;
 
-       cpumask_clear_cpu(cpu, nohz_cpu_mask);
        ts->idle_waketime = now;
 
        local_irq_save(flags);
@@ -389,9 +388,6 @@ void tick_nohz_stop_sched_tick(int inidle)
                else
                        expires.tv64 = KTIME_MAX;
 
-               if (delta_jiffies > 1)
-                       cpumask_set_cpu(cpu, nohz_cpu_mask);
-
                /* Skip reprogram of event if its not changed */
                if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
                        goto out;
@@ -441,7 +437,6 @@ void tick_nohz_stop_sched_tick(int inidle)
                 * softirq.
                 */
                tick_do_update_jiffies64(ktime_get());
-               cpumask_clear_cpu(cpu, nohz_cpu_mask);
        }
        raise_softirq_irqoff(TIMER_SOFTIRQ);
 out:
@@ -524,7 +519,6 @@ void tick_nohz_restart_sched_tick(void)
        /* Update jiffies first */
        select_nohz_load_balancer(0);
        tick_do_update_jiffies64(now);
-       cpumask_clear_cpu(cpu, nohz_cpu_mask);
 
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
        /*