From: Anders Berg <anders.b...@intel.com>
Fix sched_clock setup to handle conversions of sched_clock when the frequency
of the clock doesn't evenly divide NSEC_PER_SEC.
To handle this, the conversion from clock ticks to nanoseconds must be done via
a multiplication and a shift (to avoid divide). The appropriate multiplication
and shift factors are computed using the helper from kernel/clocksource.c
Signed-off-by: Anders Berg <anders.b...@intel.com>
---
arch/arm/kernel/arch_timer.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index 59dcdce..2726855 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -23,10 +23,12 @@ static unsigned long arch_timer_read_counter_long(void)
}
static u32 sched_clock_mult __read_mostly;
+static u32 sched_clock_shift __read_mostly;
static unsigned long long notrace arch_timer_sched_clock(void)
{
- return arch_timer_read_counter() * sched_clock_mult;
+ unsigned long long tmp = arch_timer_read_counter();
+ return (tmp * sched_clock_mult) >> sched_clock_shift;
}
static struct delay_timer arch_delay_timer;
@@ -41,15 +43,25 @@ static void __init arch_timer_delay_timer_register(void)
int __init arch_timer_arch_init(void)
{
- u32 arch_timer_rate = arch_timer_get_rate();
+ u32 arch_timer_rate = arch_timer_get_rate();
+ u64 maxsec;
if (arch_timer_rate == 0)
return -ENXIO;
arch_timer_delay_timer_register();
- /* Cache the sched_clock multiplier to save a divide in the hot path. */
- sched_clock_mult = NSEC_PER_SEC / arch_timer_rate;
+ /* Select maxsec so we get a large conversion range (56 bits) for the
+ * mult/shift while making sure the resulting maxsec fits in 32 bits.
+ */
+ maxsec = 1ULL << 56;
+ do_div(maxsec, arch_timer_rate);
+ if ((maxsec >> 32) != 0)
+ maxsec = 0xffffffff;
+
+ /* Cache the multiplier and shift to save a divide in the hot path. */
+ clocks_calc_mult_shift(&sched_clock_mult, &sched_clock_shift,
+ arch_timer_rate, NSEC_PER_SEC, (u32)maxsec);
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);
--
1.7.9.5
--
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