[PATCH] i386 apm.c optimization

- avoid expensive modulo (integer division) which happened
  since APM_MAX_EVENTS is 20 (non-power-of-2)
- kill compiler warnings by initializing two variables
- add __read_mostly to some important static variables that are read often
  (by idle loop etc.)
- constify several structures

Signed-off-by: Andreas Mohr <andi@lisas.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 22 insertions, 17 deletions

diff --git a/arch/i386/kernel/apm.c b/arch/i386/kernel/apm.c
index df0e1745f189..9e819eb68229 100644
--- a/arch/i386/kernel/apm.c
+++ b/arch/i386/kernel/apm.c
@@ -374,14 +374,14 @@ static struct {
         unsigned short  segment;
 }                               apm_bios_entry;
 static int                      clock_slowed;
-static int                      idle_threshold = DEFAULT_IDLE_THRESHOLD;
-static int                      idle_period = DEFAULT_IDLE_PERIOD;
+static int                      idle_threshold __read_mostly = DEFAULT_IDLE_THRESHOLD;
+static int                      idle_period __read_mostly = DEFAULT_IDLE_PERIOD;
 static int                      set_pm_idle;
 static int                      suspends_pending;
 static int                      standbys_pending;
 static int                      ignore_sys_suspend;
 static int                      ignore_normal_resume;
-static int                      bounce_interval = DEFAULT_BOUNCE_INTERVAL;
+static int                      bounce_interval __read_mostly = DEFAULT_BOUNCE_INTERVAL;
 
 #ifdef CONFIG_APM_RTC_IS_GMT
 #       define  clock_cmos_diff 0
@@ -390,8 +390,8 @@ static int			bounce_interval = DEFAULT_BOUNCE_INTERVAL;
 static long                     clock_cmos_diff;
 static int                      got_clock_diff;
 #endif
-static int                      debug;
-static int                      smp;
+static int                      debug __read_mostly;
+static int                      smp __read_mostly;
 static int                      apm_disabled = -1;
 #ifdef CONFIG_SMP
 static int                      power_off;
@@ -403,8 +403,8 @@ static int			realmode_power_off = 1;
 #else
 static int                      realmode_power_off;
 #endif
-static int                      exit_kapmd;
-static int                      kapmd_running;
+static int                      exit_kapmd __read_mostly;
+static int                      kapmd_running __read_mostly;
 #ifdef CONFIG_APM_ALLOW_INTS
 static int                      allow_ints = 1;
 #else
@@ -416,15 +416,15 @@ static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
 static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);
 static struct apm_user *        user_list;
 static DEFINE_SPINLOCK(user_list_lock);
-static struct desc_struct       bad_bios_desc = { 0, 0x00409200 };
+static const struct desc_struct bad_bios_desc = { 0, 0x00409200 };
 
-static char                     driver_version[] = "1.16ac";    /* no spaces */
+static const char               driver_version[] = "1.16ac";    /* no spaces */
 
 /*
  *      APM event names taken from the APM 1.2 specification. These are
  *      the message codes that the BIOS uses to tell us about events
  */
-static char *   apm_event_name[] = {
+static const char *     const apm_event_name[] = {
         "system standby",
         "system suspend",
         "normal resume",
@@ -616,7 +616,7 @@ static u8 apm_bios_call(u32 func, u32 ebx_in, u32 ecx_in,
  *      @ecx_in: ECX register value for BIOS call
  *      @eax: EAX register on return from the BIOS call
  *
- *      Make a BIOS call that does only returns one value, or just status.
+ *      Make a BIOS call that returns one value only, or just status.
  *      If there is an error, then the error code is returned in AH
  *      (bits 8-15 of eax) and this function returns non-zero. This is
  *      used for simpler BIOS operations. This call may hold interrupts
@@ -822,7 +822,7 @@ static void apm_do_busy(void)
 #define IDLE_CALC_LIMIT   (HZ * 100)
 #define IDLE_LEAKY_MAX    16
 
-static void (*original_pm_idle)(void);
+static void (*original_pm_idle)(void) __read_mostly;
 
 /**
  * apm_cpu_idle         -       cpu idling for APM capable Linux
@@ -1063,7 +1063,8 @@ static int apm_engage_power_management(u_short device, int enable)
  
 static int apm_console_blank(int blank)
 {
-        int error, i;
+        int error = APM_NOT_ENGAGED; /* silence gcc */
+        int i;
         u_short state;
         static const u_short dev[3] = { 0x100, 0x1FF, 0x101 };
 
@@ -1104,7 +1105,8 @@ static int queue_empty(struct apm_user *as)
 
 static apm_event_t get_queued_event(struct apm_user *as)
 {
-        as->event_tail = (as->event_tail + 1) % APM_MAX_EVENTS;
+        if (++as->event_tail >= APM_MAX_EVENTS)
+                as->event_tail = 0;
         return as->events[as->event_tail];
 }
 
@@ -1118,13 +1120,16 @@ static void queue_event(apm_event_t event, struct apm_user *sender)
         for (as = user_list; as != NULL; as = as->next) {
                 if ((as == sender) || (!as->reader))
                         continue;
-                as->event_head = (as->event_head + 1) % APM_MAX_EVENTS;
+                if (++as->event_head >= APM_MAX_EVENTS)
+                        as->event_head = 0;
+
                 if (as->event_head == as->event_tail) {
                         static int notified;
 
                         if (notified++ == 0)
                             printk(KERN_ERR "apm: an event queue overflowed\n");
-                        as->event_tail = (as->event_tail + 1) % APM_MAX_EVENTS;
+                        if (++as->event_tail >= APM_MAX_EVENTS)
+                                as->event_tail = 0;
                 }
                 as->events[as->event_head] = event;
                 if ((!as->suser) || (!as->writer))
@@ -1282,7 +1287,7 @@ static void standby(void)
 static apm_event_t get_event(void)
 {
         int             error;
-        apm_event_t     event;
+        apm_event_t     event = APM_NO_EVENTS; /* silence gcc */
         apm_eventinfo_t info;
 
         static int notified;