Commit 613f5d13 authored May 06, 2013 by Colin Cross Committed by Rafael J. Wysocki May 12, 2013

freezer: skip waking up tasks with PF_FREEZER_SKIP set



Android goes through suspend/resume very often (every few seconds when
on a busy wifi network with the screen off), and a significant portion
of the energy used to go in and out of suspend is spent in the
freezer.  If a task has called freezer_do_not_count(), don't bother
waking it up.  If it happens to wake up later it will call
freezer_count() and immediately enter the refrigerator.

Combined with patches to convert freezable helpers to use
freezer_do_not_count() and convert common sites where idle userspace
tasks are blocked to use the freezable helpers, this reduces the
time and energy required to suspend and resume.

Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent 18ad0c62

kernel/freezer.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -110,6 +110,18 @@ bool freeze_task(struct task_struct *p)
		{
		unsigned long flags;

		/*
		* This check can race with freezer_do_not_count, but worst case that
		* will result in an extra wakeup being sent to the task. It does not
		* race with freezer_count(), the barriers in freezer_count() and
		* freezer_should_skip() ensure that either freezer_count() sees
		* freezing == true in try_to_freeze() and freezes, or
		* freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
		* normally.
		*/
		if (freezer_should_skip(p))
		return false;

		spin_lock_irqsave(&freezer_lock, flags);
		if (!freezing(p) \|\| frozen(p)) {
		spin_unlock_irqrestore(&freezer_lock, flags);