[lkml]   [2013]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH v2 02/10] 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.

Signed-off-by: Colin Cross <>
v2: move check to freeze_task()

kernel/freezer.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index c38893b..8b2afc1 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);

 \ /
  Last update: 2013-05-02 03:41    [W:0.199 / U:9.996 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site