[RFC PATCH 01/11] nohz,time: make account_process_tick work on the task's CPU

[riel@redhat.com]

From: Rik van Riel <riel@redhat.com>

Teach account_process_tick to work on the CPU of the task
specified in the function argument. This allows us to do
remote tick based sampling of a nohz_full cpu from a
housekeeping CPU.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 kernel/sched/cputime.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 8394b1ee600c..97077c282626 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -463,8 +463,14 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
 void account_process_tick(struct task_struct *p, int user_tick)
 {
 	cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
-	struct rq *rq = this_rq();
+	int cpu = task_cpu(p);
+	struct rq *rq = cpu_rq(cpu);
 
+	/*
+	 * Tests current CPU, not "cpu", to see whether account_process_tick()
+	 * should do work on this invocation, or whether time keeping for
+	 * this CPU is done in some other way.
+	 */
 	if (vtime_accounting_enabled())
 		return;
 
-- 
2.1.0