diff options
authorColin Cross <ccross@android.com>2013-05-06 23:50:11 +0000
committerArve Hjønnevåg <arve@android.com>2013-07-01 15:40:39 -0700
commit44e77f70f60bdbea4c2b833ae895d6c0357953f4 (patch)
parenta57d997d090d0abe8317dca02320ea08bb773e80 (diff)
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. Change-Id: I6ba019d24273619849af757a413271da3261d7db 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>
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c
index c38893b0efb..8b2afc1c9df 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -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);