From c1de45ca831acee9b72c9320dde447edafadb43f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 28 Nov 2016 23:03:05 -0800 Subject: sched/idle: Add support for tasks that inject idle Idle injection drivers such as Intel powerclamp and ACPI PAD drivers use realtime tasks to take control of CPU then inject idle. There are two issues with this approach: 1. Low efficiency: injected idle task is treated as busy so sched ticks do not stop during injected idle period, the result of these unwanted wakeups can be ~20% loss in power savings. 2. Idle accounting: injected idle time is presented to user as busy. This patch addresses the issues by introducing a new PF_IDLE flag which allows any given task to be treated as idle task while the flag is set. Therefore, idle injection tasks can run through the normal flow of NOHZ idle enter/exit to get the correct accounting as well as tick stop when possible. The implication is that idle task is then no longer limited to PID == 0. Acked-by: Ingo Molnar Signed-off-by: Peter Zijlstra Signed-off-by: Jacob Pan Signed-off-by: Rafael J. Wysocki --- kernel/sched/core.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/sched/core.c') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 94732d1..63b3a8a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5285,6 +5285,7 @@ void init_idle(struct task_struct *idle, int cpu) __sched_fork(0, idle); idle->state = TASK_RUNNING; idle->se.exec_start = sched_clock(); + idle->flags |= PF_IDLE; kasan_unpoison_task_stack(idle); -- cgit v1.1