linux-kernel - [PATCH 1/3] hrtimer: make the futex() system call use the per process slack value

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Date:	Wed, 10 Sep 2008 20:28:50 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	linux-kernel@...r.kernel.org
Cc:	Arjan van de Ven <arjan@...radead.org>, mingo@...e.hu,
	peterz@...radead.org
Subject: [PATCH 1/3] hrtimer: make the futex() system call use the per
 process slack value


From: Arjan van de Ven <arjan@...ux.intel.com>
Subject: [PATCH] hrtimer: make the futex() system call use the per process slack value

This patch makes the futex() system call use the per process
slack value; with this users are able to externally control existing
applications to reduce the wakeup rate.

Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
---
 kernel/futex.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 4cd5b43..8af1002 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1296,10 +1296,14 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
 		if (!abs_time)
 			schedule();
 		else {
+			unsigned long slack;
+			slack = current->timer_slack_ns;
+			if (rt_task(current))
+				slack = 0;
 			hrtimer_init_on_stack(&t.timer, CLOCK_MONOTONIC,
 						HRTIMER_MODE_ABS);
 			hrtimer_init_sleeper(&t, current);
-			hrtimer_set_expires(&t.timer, *abs_time);
+			hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack);
 
 			hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS);
 			if (!hrtimer_active(&t.timer))
-- 
1.5.5.1



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
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