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Message-Id: <1367884221-20462-7-git-send-email-ccross@android.com>
Date: Mon, 6 May 2013 16:50:11 -0700
From: Colin Cross <ccross@...roid.com>
To: linux-kernel@...r.kernel.org
Cc: Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mandeep Singh Baines <msb@...omium.org>,
Colin Cross <ccross@...roid.com>,
Oleg Nesterov <oleg@...hat.com>, linux-nfs@...r.kernel.org,
linux-pm@...r.kernel.org, netdev@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>
Subject: [PATCH v3 06/16] 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@...nel.org>
Acked-by: Pavel Machek <pavel@....cz>
Signed-off-by: Colin Cross <ccross@...roid.com>
---
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);
--
1.8.2.1
--
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