[PATCH] -mm: acpi idle __read_mostly and de-init static var

[PATCH] -mm: acpi idle __read_mostly and de-init static var

[Andreas Mohr]

Hello all,

- make pm_idle_save, nocst and bm_history __read_mostly
- static first_run is initialized to 0 by default already
- don't remove static init value of nocst and bm_history
  since __read_mostly may be special
  (see e.g. http://www.ussg.iu.edu/hypermail/linux/kernel/0010.0/0771.html)

Patch tested on 2.6.17-rc1-mm2, rediffed against 2.6.17-rc1-mm3.

Signed-off-by: Andreas Mohr <andi@lisas.de>


diff -urN linux-2.6.17-rc1-mm3.orig/drivers/acpi/processor_idle.c linux-2.6.17-rc1-mm3/drivers/acpi/processor_idle.c
--- linux-2.6.17-rc1-mm3.orig/drivers/acpi/processor_idle.c	2006-04-18 20:06:57.000000000 +0200
+++ linux-2.6.17-rc1-mm3/drivers/acpi/processor_idle.c	2006-04-18 20:11:16.000000000 +0200
@@ -54,10 +54,10 @@
 #define US_TO_PM_TIMER_TICKS(t)		((t * (PM_TIMER_FREQUENCY/1000)) / 1000)
 #define C2_OVERHEAD			4	/* 1us (3.579 ticks per us) */
 #define C3_OVERHEAD			4	/* 1us (3.579 ticks per us) */
-static void (*pm_idle_save) (void);
+static void (*pm_idle_save) (void) __read_mostly;
 module_param(max_cstate, uint, 0644);
 
-static unsigned int nocst = 0;
+static unsigned int nocst __read_mostly = 0;
 module_param(nocst, uint, 0000);
 
 /*
@@ -67,7 +67,7 @@
  * 100 HZ: 0x0000000F: 4 jiffies = 40ms
  * reduce history for more aggressive entry into C3
  */
-static unsigned int bm_history =
+static unsigned int bm_history __read_mostly =
     (HZ >= 800 ? 0xFFFFFFFF : ((1U << (HZ / 25)) - 1));
 module_param(bm_history, uint, 0644);
 /* --------------------------------------------------------------------------
@@ -1088,7 +1088,7 @@
 			      struct acpi_device *device)
 {
 	acpi_status status = 0;
-	static int first_run = 0;
+	static int first_run; /* static: = 0 */
 	struct proc_dir_entry *entry = NULL;
 	unsigned int i;
 

Re: [PATCH] -mm: acpi idle __read_mostly and de-init static var

[Andrew Morton]

Andreas Mohr <andi@rhlx01.fht-esslingen.de> wrote:
>
> - don't remove static init value of nocst and bm_history
>    since __read_mostly may be special
>    (see e.g. http://www.ussg.iu.edu/hypermail/linux/kernel/0010.0/0771.html)
> 

hm, that was six years ago.  I'm vaguely surprised that the initialisation
was needed even then.  It isn't needed now.  Or if it is, we need to find
out why and fix it.

Re: [PATCH] -mm: acpi idle __read_mostly and de-init static var

[Roman Zippel]

Hi,

On Tue, 18 Apr 2006, Andrew Morton wrote:

> Andreas Mohr <andi@rhlx01.fht-esslingen.de> wrote:
> >
> > - don't remove static init value of nocst and bm_history
> >    since __read_mostly may be special
> >    (see e.g. http://www.ussg.iu.edu/hypermail/linux/kernel/0010.0/0771.html)
> > 
> 
> hm, that was six years ago.  I'm vaguely surprised that the initialisation
> was needed even then.  It isn't needed now.  Or if it is, we need to find
> out why and fix it.

I guess 2.7.2 was still a valid compiler then. :)
All later versions don't behave like this, although it's still documented 
like this: http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html

bye, Roman