From 7811fb8f400a3dbfa027d86bb583a31c66fddfc3 Mon Sep 17 00:00:00 2001 From: Clemens Ladisch Date: Sun, 30 Oct 2005 15:03:36 -0800 Subject: [PATCH] [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 Acked-by: Venkatesh Pallipadi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/time_hpet.c | 5 ++++- arch/x86_64/kernel/time.c | 5 ++++- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/i386/kernel/time_hpet.c b/arch/i386/kernel/time_hpet.c index cb1f313858..9caeaa315c 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; } /* diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 35a896ef4c..fdaddc4e52 100644 --- a/arch/x86_64/kernel/time.c +++ b/arch/x86_64/kernel/time.c @@ -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; } /* -- 2.39.5