linux-kernel - [PATCH v3 5/6] timerfd: Add support for deferrable timers

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Date:	Thu, 20 Feb 2014 12:40:32 +0400
From:	Alexey Perevalov <a.perevalov@...sung.com>
To:	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	john.stultz@...aro.org
Cc:	Anton Vorontsov <anton@...msg.org>, anton@...sg.org,
	kyungmin.park@...sung.com, cw00.choi@...sung.com,
	akpm@...ux-foundation.org,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Alexey Perevalov <a.perevalov@...sung.com>
Subject: [PATCH v3 5/6] timerfd: Add support for deferrable timers

From: Anton Vorontsov <anton@...msg.org>

This patch implements a userland-side API for generic deferrable timers,
per linux/timer.h:

 * A deferrable timer will work normally when the system is busy, but
 * will not cause a CPU to come out of idle just to service it; instead,
 * the timer will be serviced when the CPU eventually wakes up with a
 * subsequent non-deferrable timer.

These timers are crucial for power saving, i.e. periodic tasks that want
to work in background when the system is under use, but don't want to
cause wakeups themselves.

The deferred timers are somewhat orthogonal to high-res external timers,
since the deferred timer is tied to the system load, not just to some
external decrementer source.

Currently, the implementation is based on high resolution timers.

Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
Signed-off-by: Alexey Perevalov <a.perevalov@...sung.com>
---
 fs/timerfd.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 3561ce7..c132fd2 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -231,7 +231,7 @@ static unsigned int timerfd_poll(struct file *file, poll_table *wait)
 
 static u64 timerfd_rearm(struct timerfd_ctx *ctx)
 {
-	u64 orun;
+	u64 orun = 0;
 
 	if (isalarm(ctx)) {
 		orun += alarm_forward_now(
@@ -326,7 +326,10 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	    (clockid != CLOCK_MONOTONIC &&
 	     clockid != CLOCK_REALTIME &&
 	     clockid != CLOCK_REALTIME_ALARM &&
-	     clockid != CLOCK_BOOTTIME_ALARM))
+	     clockid != CLOCK_BOOTTIME_ALARM &&
+	     clockid != CLOCK_REALTIME_DEFERRABLE &&
+	     clockid != CLOCK_MONOTONIC_DEFERRABLE &&
+	     clockid != CLOCK_BOOTTIME_DEFERRABLE))
 		return -EINVAL;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
@@ -354,7 +357,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	return ufd;
 }
 
-static int do_timerfd_settime(int ufd, int flags, 
+static int do_timerfd_settime(int ufd, int flags,
 		const struct itimerspec *new,
 		struct itimerspec *old)
 {
-- 
1.7.9.5

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