Re: MSEC_TO_JIFFIES is messed up...

[Ingo Molnar <mingo@elte.hu>]

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* Valdis.Kletnieks@vt.edu <Valdis.Kletnieks@vt.edu> wrote:

> The problem is that even for the i386 family, there's no inherent
> reason why the value of HZ is nailed to 1000 [...]

The code is 100% correct, but not 100% clean, and definitely not
documented. The reason for the change was to avoid unnecessary integer
multiplications and divisions in sched.c.

the attached patch (against BK-curr) cleans this up and makes the
defines generic and arch-independent.

	Ingo

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--- linux/include/linux/time.h.orig	
+++ linux/include/linux/time.h	
@@ -177,6 +177,15 @@ struct timezone {
 	(SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1)
 
 #endif
+
+#if HZ == 1000
+# define JIFFIES_TO_MSEC(x)	(x)
+# define MSEC_TO_JIFFIES(x)	(x)
+#else
+# define JIFFIES_TO_MSEC(x)	((x) * 1000 / HZ)
+# define MSEC_TO_JIFFIES(x)	((x) * HZ / 1000)
+#endif
+
 /*
  * The TICK_NSEC - 1 rounds up the value to the next resolution.  Note
  * that a remainder subtract here would not do the right thing as the
--- linux/include/asm-i386/param.h.orig	
+++ linux/include/asm-i386/param.h	
@@ -5,8 +5,6 @@
 # define HZ		1000		/* Internal kernel timer frequency */
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC		(USER_HZ)	/* like times() */
-# define JIFFIES_TO_MSEC(x)	(x)
-# define MSEC_TO_JIFFIES(x)	(x)
 #endif
 
 #ifndef HZ
--- linux/kernel/sched.c.orig	
+++ linux/kernel/sched.c	
@@ -75,13 +75,6 @@
 #define NS_TO_JIFFIES(TIME)	((TIME) / (1000000000 / HZ))
 #define JIFFIES_TO_NS(TIME)	((TIME) * (1000000000 / HZ))
 
-#ifndef JIFFIES_TO_MSEC
-# define JIFFIES_TO_MSEC(x) ((x) * 1000 / HZ)
-#endif
-#ifndef MSEC_TO_JIFFIES
-# define MSEC_TO_JIFFIES(x) ((x) * HZ / 1000)
-#endif
-
 /*
  * These are the 'tuning knobs' of the scheduler:
  *