Commit-ID: 3bbfafb77a06327fa1bc9f19bc55b5c558475091
Gitweb: http://git.kernel.org/tip/3bbfafb77a06327fa1bc9f19bc55b5c558475091
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 24 Jul 2015 16:34:32 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 3 Aug 2015 11:34:16 +0200
x86, tsc, locking/static_keys: Employ static_branch_likely()
Because of the static_key restrictions we had to take an unconditional
jump for the most likely case, causing $I bloat.
Rewrite to use the new primitives.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/tsc.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 1bb8bab..b9cfd46 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -38,7 +38,7 @@ 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;
+static DEFINE_STATIC_KEY_FALSE(__use_tsc);
int tsc_clocksource_reliable;
@@ -274,7 +274,12 @@ done:
*/
u64 native_sched_clock(void)
{
- u64 tsc_now;
+ if (static_branch_likely(&__use_tsc)) {
+ u64 tsc_now = rdtsc();
+
+ /* return the value in ns */
+ return cycles_2_ns(tsc_now);
+ }
/*
* Fall back to jiffies if there's no TSC available:
@@ -284,16 +289,9 @@ u64 native_sched_clock(void)
* very important for it to be as fast as the platform
* can achieve it. )
*/
- 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);
- }
-
- /* read the Time Stamp Counter: */
- tsc_now = rdtsc();
- /* return the value in ns */
- return cycles_2_ns(tsc_now);
+ /* No locking but a rare wrong value is not a big deal: */
+ return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
}
/* We need to define a real function for sched_clock, to override the
@@ -1204,7 +1202,7 @@ void __init tsc_init(void)
/* now allow native_sched_clock() to use rdtsc */
tsc_disabled = 0;
- static_key_slow_inc(&__use_tsc);
+ static_branch_enable(&__use_tsc);
if (!no_sched_irq_time)
enable_sched_clock_irqtime();
--
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