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ARM: arch_timer: use full 64-bit counter for sched_clock

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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 <rob.herring@calxeda.com>
This commit is contained in:
Rob Herring 2013-03-11 16:23:46 -05:00
parent 7e48c0b9d9
commit 023796b9be
1 changed files with 13 additions and 5 deletions
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18
arch/arm/kernel/arch_timer.c
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@ -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;
}