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authorClemens Ladisch <clemens@ladisch.de>2005-10-30 15:03:36 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-30 17:37:30 -0800
commit7811fb8f400a3dbfa027d86bb583a31c66fddfc3 (patch)
tree2df816ff6559a0e2f9d7537e1accdfe932e027d4 /arch/i386/kernel
parent5f819949ee4e5a06c2e0054cbb42f3f0d170d779 (diff)
[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>
Diffstat (limited to 'arch/i386/kernel')
-rw-r--r--arch/i386/kernel/time_hpet.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/i386/kernel/time_hpet.c b/arch/i386/kernel/time_hpet.c
index cb1f313858e3..9caeaa315cd7 100644
--- a/arch/i386/kernel/time_hpet.c
+++ b/arch/i386/kernel/time_hpet.c
@@ -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;
}
/*