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SubjectPatch 3/3: Reduce number of get_cmos_time_calls.
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Date
Create new __get_cmos_time patch, which doesn't wait for the start of a
new second before returning. Adjust timer_suspend to use this as we
don't appear to need the exact start of a second when suspending.

Signed-off-by: Nigel Cunningham <ncunningham@linuxmail.org>

diff -ruNp 913-old/arch/i386/kernel/time.c 913-new/arch/i386/kernel/time.c
--- 913-old/arch/i386/kernel/time.c 2005-01-08 19:40:06.149971536 +1100
+++ 913-new/arch/i386/kernel/time.c 2005-01-08 19:39:51.915135560 +1100
@@ -327,7 +327,7 @@ static int timer_suspend(struct sys_devi
/*
* Estimate time zone so that set_time can update the clock
*/
- long cmos_time = get_cmos_time();
+ long cmos_time = __get_cmos_time();

clock_cmos_diff = -cmos_time;
clock_cmos_diff += get_seconds();
diff -ruNp 913-old/arch/x86_64/kernel/time.c 913-new/arch/x86_64/kernel/time.c
--- 913-old/arch/x86_64/kernel/time.c 2004-12-10 14:27:08.000000000 +1100
+++ 913-new/arch/x86_64/kernel/time.c 2005-01-08 19:39:24.664278320 +1100
@@ -499,11 +499,56 @@ unsigned long long sched_clock(void)
return cycles_2_ns(a);
}

+unsigned long __get_cmos_time(void)
+{
+ unsigned int year, mon, day, hour, min, sec;
+
+ /*
+ * Do we need the spinlock in here too?
+ *
+ * If we're called directly (not via get_cmos_time),
+ * we're in the middle of a sysdev suspend/resume
+ * and interrupts are disabled, so this
+ * should be safe without any locking.
+ * -- NC
+ */
+
+ do {
+ sec = CMOS_READ(RTC_SECONDS);
+ min = CMOS_READ(RTC_MINUTES);
+ hour = CMOS_READ(RTC_HOURS);
+ day = CMOS_READ(RTC_DAY_OF_MONTH);
+ mon = CMOS_READ(RTC_MONTH);
+ year = CMOS_READ(RTC_YEAR);
+ } while (sec != CMOS_READ(RTC_SECONDS));
+
+ /*
+ * We know that x86-64 always uses BCD format, no need to check the config
+ * register.
+ */
+
+ BCD_TO_BIN(sec);
+ BCD_TO_BIN(min);
+ BCD_TO_BIN(hour);
+ BCD_TO_BIN(day);
+ BCD_TO_BIN(mon);
+ BCD_TO_BIN(year);
+
+ /*
+ * This will work up to Dec 31, 2069.
+ */
+
+ if ((year += 1900) < 1970)
+ year += 100;
+
+ return mktime(year, mon, day, hour, min, sec);
+}
+
unsigned long get_cmos_time(void)
{
- unsigned int timeout, year, mon, day, hour, min, sec;
+ unsigned int timeout;
unsigned char last, this;
- unsigned long flags;
+ unsigned long flags, result;

/*
* The Linux interpretation of the CMOS clock register contents: When the
@@ -524,40 +569,11 @@ unsigned long get_cmos_time(void)
timeout--;
}

-/*
- * Here we are safe to assume the registers won't change for a whole second, so
- * we just go ahead and read them.
- */
-
- sec = CMOS_READ(RTC_SECONDS);
- min = CMOS_READ(RTC_MINUTES);
- hour = CMOS_READ(RTC_HOURS);
- day = CMOS_READ(RTC_DAY_OF_MONTH);
- mon = CMOS_READ(RTC_MONTH);
- year = CMOS_READ(RTC_YEAR);
-
+ result = __get_cmos_time();
spin_unlock_irqrestore(&rtc_lock, flags);

-/*
- * We know that x86-64 always uses BCD format, no need to check the config
- * register.
- */
-
- BCD_TO_BIN(sec);
- BCD_TO_BIN(min);
- BCD_TO_BIN(hour);
- BCD_TO_BIN(day);
- BCD_TO_BIN(mon);
- BCD_TO_BIN(year);
+ return result;

-/*
- * This will work up to Dec 31, 2069.
- */
-
- if ((year += 1900) < 1970)
- year += 100;
-
- return mktime(year, mon, day, hour, min, sec);
}

#ifdef CONFIG_CPU_FREQ
@@ -962,7 +978,7 @@ static int timer_suspend(struct sys_devi
/*
* Estimate time zone so that set_time can update the clock
*/
- clock_cmos_diff = -get_cmos_time();
+ clock_cmos_diff = -__get_cmos_time();
clock_cmos_diff += get_seconds();
return 0;
}
diff -ruNp 913-old/include/asm-i386/mach-default/mach_time.h 913-new/include/asm-i386/mach-default/mach_time.h
--- 913-old/include/asm-i386/mach-default/mach_time.h 2004-11-03 21:53:12.000000000 +1100
+++ 913-new/include/asm-i386/mach-default/mach_time.h 2005-01-08 19:39:24.676276496 +1100
@@ -79,24 +79,19 @@ static inline int mach_set_rtc_mmss(unsi
return retval;
}

-static inline unsigned long mach_get_cmos_time(void)
+/* __get_cmos_time
+ *
+ * Separated out from mach_get_cmos_time so that we can
+ * quickly get the cmos time when we don't care about
+ * whether the second has just started.
+ *
+ * Used from suspend and resume sysdev calls.
+ */
+static inline unsigned long __get_cmos_time(void)
{
unsigned int year, mon, day, hour, min, sec;
- int i;

- /* The Linux interpretation of the CMOS clock register contents:
- * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
- * RTC registers show the second which has precisely just started.
- * Let's hope other operating systems interpret the RTC the same way.
- */
- /* read RTC exactly on falling edge of update flag */
- for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
- if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
- break;
- for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
- if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
- break;
- do { /* Isn't this overkill ? UIP above should guarantee consistency */
+ do {
sec = CMOS_READ(RTC_SECONDS);
min = CMOS_READ(RTC_MINUTES);
hour = CMOS_READ(RTC_HOURS);
@@ -104,6 +99,7 @@ static inline unsigned long mach_get_cmo
mon = CMOS_READ(RTC_MONTH);
year = CMOS_READ(RTC_YEAR);
} while (sec != CMOS_READ(RTC_SECONDS));
+
if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
{
BCD_TO_BIN(sec);
@@ -119,4 +115,24 @@ static inline unsigned long mach_get_cmo
return mktime(year, mon, day, hour, min, sec);
}

+static inline unsigned long mach_get_cmos_time(void)
+{
+ int i;
+
+ /* The Linux interpretation of the CMOS clock register contents:
+ * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
+ * RTC registers show the second which has precisely just started.
+ * Let's hope other operating systems interpret the RTC the same way.
+ */
+ /* read RTC exactly on falling edge of update flag */
+ for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
+ if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
+ break;
+ for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
+ if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
+ break;
+
+ return __get_cmos_time();
+}
+
#endif /* !_MACH_TIME_H */

-
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