Messages in this thread Patch in this message | | | Date | Thu, 12 Dec 2013 15:08:50 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 15/15] x86: Avoid a runtime condition in native_sched_clock() |
| |
Use a static_key to avoid touching tsc_disabled and a runtime condition in native_sched_clock() -- less cachelines touched is always better.
MAINLINE PRE POST
sched_clock_stable: 1 1 1 (cold) sched_clock: 329841 215295 213039 (cold) local_clock: 301773 220773 216084 (warm) sched_clock: 38375 25659 25231 (warm) local_clock: 100371 27242 27601 (warm) rdtsc: 27340 24208 24203 sched_clock_stable: 0 0 0 (cold) sched_clock: 382634 237019 240055 (cold) local_clock: 396890 294819 299942 (warm) sched_clock: 38194 25609 25276 (warm) local_clock: 143452 71232 73232 (warm) rdtsc: 27345 24243 24244
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; /* @@ -243,7 +246,7 @@ 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); } @@ -1152,7 +1155,9 @@ 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();
| |