linux-kernel - [RFC] Use jiffies_64 in sched

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Message-ID: <20061229155216.GA11125@localhost.sw.ru>
Date:	Fri, 29 Dec 2006 18:52:16 +0300
From:	Alexey Dobriyan <adobriyan@...nvz.org>
To:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Cc:	devel@...nvz.org
Subject: [RFC] Use jiffies_64 in sched_clock()

Would it make sense to always use jiffies_64 instead of jiffies?
(module hardware specific version)

This is what FRV, UML, one ia64 version, one i386 version do.

Also substract initial jiffies.

Signed-off-by: Alexey Dobriyan <adobriyan@...nvz.org>
---

 arch/frv/kernel/time.c |    8 --------
 arch/um/kernel/time.c  |    8 --------
 kernel/sched.c         |    3 ++-
 3 files changed, 2 insertions(+), 17 deletions(-)

--- a/arch/frv/kernel/time.c
+++ b/arch/frv/kernel/time.c
@@ -139,11 +139,3 @@ void time_init(void)
 
 	time_divisor_init();
 }
-
-/*
- * Scheduler clock - returns current time in nanosec units.
- */
-unsigned long long sched_clock(void)
-{
-	return jiffies_64 * (1000000000 / HZ);
-}
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -27,14 +27,6 @@ int hz(void)
 	return(HZ);
 }
 
-/*
- * Scheduler clock - returns current time in nanosec units.
- */
-unsigned long long sched_clock(void)
-{
-	return (unsigned long long)jiffies_64 * (1000000000 / HZ);
-}
-
 static unsigned long long prev_nsecs;
 #ifdef CONFIG_UML_REAL_TIME_CLOCK
 static long long delta;   		/* Deviation per interval */
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -64,7 +64,8 @@ #include <asm/unistd.h>
  */
 unsigned long long __attribute__((weak)) sched_clock(void)
 {
-	return (unsigned long long)jiffies * (1000000000 / HZ);
+	/* No locking but a rare wrong value is not a big deal. */
+	return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
 }
 
 /*

-
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