[RFC PATCH 08/11] nohz,timer: have housekeeper call account_process_tick for nohz cpus

[riel]

From: Rik van Riel <riel@xxxxxxxxxx>

Have the housekeeper CPU call account_process_tick to do tick based
accounting for remote nohz_full CPUs.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
---
 kernel/time/timer.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 2ece3aa5069c..6adebb373317 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -42,6 +42,7 @@
 #include <linux/sched/sysctl.h>
 #include <linux/slab.h>
 #include <linux/compat.h>
+#include "../sched/sched.h"
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -1382,6 +1383,29 @@ unsigned long get_next_timer_interrupt(unsigned long now)
 }
 #endif
 
+#ifdef CONFIG_NO_HZ_FULL
+static void account_remote_process_ticks(void)
+{
+	int cpu;
+
+	/*
+	 * The current task on another CPU can get rescheduled while
+	 * we are updating the statistics. The rcu read lock ensures
+	 * the task does not get freed, so at worst the statistics will
+	 * be off a little bit, which is expected with tick based sampling.
+	 */
+	rcu_read_lock();
+	for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask) {
+		struct task_struct *p = cpu_curr(cpu);
+		int user_tick = (per_cpu(context_tracking.state, cpu) ==
+					CONTEXT_USER);
+		
+		account_process_tick(p, user_tick);
+	}
+	rcu_read_unlock();
+}
+#endif
+
 /*
  * Called from the timer interrupt handler to charge one tick to the current
  * process.  user_tick is 1 if the tick is user time, 0 for system.
@@ -1392,6 +1416,10 @@ void update_process_times(int user_tick)
 
 	/* Note: this timer irq context must be accounted for as well. */
 	account_process_tick(p, user_tick);
+#ifdef CONFIG_NO_HZ_FULL
+	if (is_timer_housekeeping_cpu(smp_processor_id()))
+		account_remote_process_ticks();
+#endif
 	run_local_timers();
 	rcu_check_callbacks(user_tick);
 #ifdef CONFIG_IRQ_WORK
-- 
2.1.0

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