Messages in this thread Patch in this message | | | Date | Fri, 29 Nov 2013 18:37:00 +0100 | From | Peter Zijlstra <> | Subject | [RFC][PATCH 3/7] x86: Avoid a runtime condition in native_sched_clock() |
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Use a static_key to avoid a runtime condition in native_sched_clock().
XXX: I still think tsc_disabled should die a horrid death.
Signed-off-by: Peter Zijlstra <peterz@infradead.org> --- arch/x86/kernel/tsc.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -11,6 +11,7 @@ #include <linux/clocksource.h> #include <linux/percpu.h> #include <linux/timex.h> +#include <linux/static_key.h> #include <asm/hpet.h> #include <asm/timer.h> @@ -37,6 +38,8 @@ static int __read_mostly tsc_unstable; erroneous rdtsc usage on !cpu_has_tsc processors */ static int __read_mostly tsc_disabled = -1; +static struct static_key __use_tsc = STATIC_KEY_INIT; + int tsc_clocksource_reliable; /* * Scheduler clock - returns current time in nanosec units. @@ -53,7 +56,7 @@ u64 native_sched_clock(void) * very important for it to be as fast as the platform * can achieve it. ) */ - if (unlikely(tsc_disabled)) { + if (static_key_false(&__use_tsc)) { /* No locking but a rare wrong value is not a big deal: */ return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ); } @@ -1002,7 +1005,9 @@ void __init tsc_init(void) return; /* now allow native_sched_clock() to use rdtsc */ + tsc_disabled = 0; + static_key_slow_inc(&__use_tsc); if (!no_sched_irq_time) enable_sched_clock_irqtime();
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