From 023796b9be3a77481cd5ee0b64a13a55bb0d5df4 Mon Sep 17 00:00:00 2001 From: Rob Herring Date: Mon, 11 Mar 2013 16:23:46 -0500 Subject: ARM: arch_timer: use full 64-bit counter for sched_clock Only 32-bits of the arch timer were being used and wrapping was needlessly being done in s/w. By using the full counter (56-64 bits), we don't need to deal with wrapping and can simplify the implementation when using arch timer. Signed-off-by: Rob Herring --- arch/arm/kernel/arch_timer.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'arch/arm/kernel/arch_timer.c') diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c index d957a51435d8..80c458fc4a30 100644 --- a/arch/arm/kernel/arch_timer.c +++ b/arch/arm/kernel/arch_timer.c @@ -22,9 +22,11 @@ static unsigned long arch_timer_read_counter_long(void) return arch_timer_read_counter(); } -static u32 arch_timer_read_counter_u32(void) +static u32 sched_clock_mult __read_mostly; + +static unsigned long long notrace arch_timer_sched_clock(void) { - return arch_timer_read_counter(); + return arch_timer_read_counter() * sched_clock_mult; } static struct delay_timer arch_delay_timer; @@ -52,10 +54,16 @@ int __init arch_timer_of_register(void) int __init arch_timer_sched_clock_init(void) { - if (arch_timer_get_rate() == 0) + u32 arch_timer_rate = arch_timer_get_rate(); + + if (arch_timer_rate == 0) return -ENXIO; - setup_sched_clock(arch_timer_read_counter_u32, - 32, arch_timer_get_rate()); + /* Cache the sched_clock multiplier to save a divide in the hot path. */ + sched_clock_mult = NSEC_PER_SEC / arch_timer_rate; + sched_clock_func = arch_timer_sched_clock; + pr_info("sched_clock: ARM arch timer >56 bits at %ukHz, resolution %uns\n", + arch_timer_rate / 1000, sched_clock_mult); + return 0; } -- cgit v1.2.3-59-g8ed1b