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[PATCH] hpet-RTC: cache the comparator register 

Reads from an HPET register require a round trip to the south bridge and are
almost as slow as PCI reads.  By caching the last value we've written to the
comparator register, we can eliminate all HPET reads from the fast path in the
emulated RTC interrupt handler.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Clemens Ladisch 2005-10-30 15:03:36 -08:00 committed by Linus Torvalds
parent 5f819949ee
commit 7811fb8f40
2 changed files with 8 additions and 2 deletions
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5
arch/i386/kernel/time_hpet.c
View File

@ -275,6 +275,7 @@ static unsigned long PIE_freq = DEFAULT_RTC_INT_FREQ;
static unsigned long PIE_count;
static unsigned long hpet_rtc_int_freq; /* RTC interrupt frequency */
static unsigned int hpet_t1_cmp; /* cached comparator register */
/*
* Timer 1 for RTC, we do not use periodic interrupt feature,
@ -306,6 +307,7 @@ int hpet_rtc_timer_init(void)
cnt = hpet_readl(HPET_COUNTER);
cnt += ((hpet_tick*HZ)/hpet_rtc_int_freq);
hpet_writel(cnt, HPET_T1_CMP);
hpet_t1_cmp = cnt;
local_irq_restore(flags);
cfg = hpet_readl(HPET_T1_CFG);
@ -333,9 +335,10 @@ static void hpet_rtc_timer_reinit(void)
hpet_rtc_int_freq = DEFAULT_RTC_INT_FREQ;
/* It is more accurate to use the comparator value than current count.*/
cnt = hpet_readl(HPET_T1_CMP);
cnt = hpet_t1_cmp;
cnt += hpet_tick*HZ/hpet_rtc_int_freq;
hpet_writel(cnt, HPET_T1_CMP);
hpet_t1_cmp = cnt;
}
/*

5
arch/x86_64/kernel/time.c
View File

@ -1089,6 +1089,7 @@ static unsigned long PIE_freq = DEFAULT_RTC_INT_FREQ;
static unsigned long PIE_count;
static unsigned long hpet_rtc_int_freq; /* RTC interrupt frequency */
static unsigned int hpet_t1_cmp; /* cached comparator register */
int is_hpet_enabled(void)
{
@ -1125,6 +1126,7 @@ int hpet_rtc_timer_init(void)
cnt = hpet_readl(HPET_COUNTER);
cnt += ((hpet_tick*HZ)/hpet_rtc_int_freq);
hpet_writel(cnt, HPET_T1_CMP);
hpet_t1_cmp = cnt;
local_irq_restore(flags);
cfg = hpet_readl(HPET_T1_CFG);
@ -1152,9 +1154,10 @@ static void hpet_rtc_timer_reinit(void)
hpet_rtc_int_freq = DEFAULT_RTC_INT_FREQ;
/* It is more accurate to use the comparator value than current count.*/
cnt = hpet_readl(HPET_T1_CMP);
cnt = hpet_t1_cmp;
cnt += hpet_tick*HZ/hpet_rtc_int_freq;
hpet_writel(cnt, HPET_T1_CMP);
hpet_t1_cmp = cnt;
}
/*