[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>

diff --git a/arch/i386/kernel/apm.c b/arch/i386/kernel/apm.c
index df0e174..9e819eb 100644 (file)
--- 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;