sched/clock, 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> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/n/tip-hrz87bo37qke25bty6pnfy4b@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -11,6 +11,7 @@
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#include <linux/clocksource.h>
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#include <linux/percpu.h>
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#include <linux/timex.h>
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#include <linux/static_key.h>
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#include <asm/hpet.h>
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#include <asm/timer.h>
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@ -37,6 +38,8 @@ static int __read_mostly tsc_unstable;
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erroneous rdtsc usage on !cpu_has_tsc processors */
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static int __read_mostly tsc_disabled = -1;
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static struct static_key __use_tsc = STATIC_KEY_INIT;
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int tsc_clocksource_reliable;
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/*
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@ -282,7 +285,7 @@ u64 native_sched_clock(void)
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* very important for it to be as fast as the platform
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* can achieve it. )
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*/
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if (unlikely(tsc_disabled)) {
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if (!static_key_false(&__use_tsc)) {
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/* No locking but a rare wrong value is not a big deal: */
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return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
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}
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@ -1193,7 +1196,9 @@ void __init tsc_init(void)
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return;
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/* now allow native_sched_clock() to use rdtsc */
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tsc_disabled = 0;
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static_key_slow_inc(&__use_tsc);
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if (!no_sched_irq_time)
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enable_sched_clock_irqtime();
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