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Subject[RFC PATCH 08/11] nohz,timer: have housekeeper call account_process_tick for nohz cpus
Date
From: Rik van Riel <riel@redhat.com>

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@redhat.com>
---
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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