Commit-ID: 10b033d434c25a6c9e0f4f4dc2418af1b8236c63
Gitweb: http://git.kernel.org/tip/10b033d434c25a6c9e0f4f4dc2418af1b8236c63
Author: Peter Zijlstra <pet...@infradead.org>
AuthorDate: Thu, 28 Nov 2013 19:01:40 +0100
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Mon, 13 Jan 2014 15:13:17 +0100
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 <pet...@infradead.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-hrz87bo37qke25bty6pnf...@git.kernel.org
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
arch/x86/kernel/tsc.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 53c1235..6377fb2 100644
--- 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;
/*
@@ -282,7 +285,7 @@ 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);
}
@@ -1193,7 +1196,9 @@ 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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