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sched/clock, x86: Use a static_key for sched_clock_stable

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In order to avoid the runtime condition and variable load turn
sched_clock_stable into a static_key.

Also provide a shorter implementation of local_clock() and
cpu_clock(int) when sched_clock_stable==1.

                        MAINLINE   PRE       POST

    sched_clock_stable: 1          1         1
    (cold) sched_clock: 329841     221876    215295
    (cold) local_clock: 301773     234692    220773
    (warm) sched_clock: 38375      25602     25659
    (warm) local_clock: 100371     33265     27242
    (warm) rdtsc:       27340      24214     24208
    sched_clock_stable: 0          0         0
    (cold) sched_clock: 382634     235941    237019
    (cold) local_clock: 396890     297017    294819
    (warm) sched_clock: 38194      25233     25609
    (warm) local_clock: 143452     71234     71232
    (warm) rdtsc:       27345      24245     24243

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-eummbdechzz37mwmpags1gjr@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2013-11-28 19:38:42 +01:00
committed by Ingo Molnar
parent ef08f0fff8
commit 35af99e646
9 changed files with 46 additions and 17 deletions
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41
kernel/sched/clock.c
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@@ -58,6 +58,7 @@
#include <linux/percpu.h>
#include <linux/ktime.h>
#include <linux/sched.h>
#include <linux/static_key.h>
/*
* Scheduler clock - returns current time in nanosec units.
@@ -74,7 +75,27 @@ EXPORT_SYMBOL_GPL(sched_clock);
__read_mostly int sched_clock_running;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
__read_mostly int sched_clock_stable;
static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
int sched_clock_stable(void)
{
if (static_key_false(&__sched_clock_stable))
return false;
return true;
}
void set_sched_clock_stable(void)
{
if (!sched_clock_stable())
static_key_slow_dec(&__sched_clock_stable);
}
void clear_sched_clock_stable(void)
{
/* XXX worry about clock continuity */
if (sched_clock_stable())
static_key_slow_inc(&__sched_clock_stable);
}
struct sched_clock_data {
u64 tick_raw;
@@ -234,7 +255,7 @@ u64 sched_clock_cpu(int cpu)
struct sched_clock_data *scd;
u64 clock;
if (sched_clock_stable)
if (sched_clock_stable())
return sched_clock();
if (unlikely(!sched_clock_running))
@@ -257,7 +278,7 @@ void sched_clock_tick(void)
struct sched_clock_data *scd;
u64 now, now_gtod;
if (sched_clock_stable)
if (sched_clock_stable())
return;
if (unlikely(!sched_clock_running))
@@ -308,7 +329,10 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
*/
u64 cpu_clock(int cpu)
{
return sched_clock_cpu(cpu);
if (static_key_false(&__sched_clock_stable))
return sched_clock_cpu(cpu);
return sched_clock();
}
/*
@@ -320,7 +344,10 @@ u64 cpu_clock(int cpu)
*/
u64 local_clock(void)
{
return sched_clock_cpu(raw_smp_processor_id());
if (static_key_false(&__sched_clock_stable))
return sched_clock_cpu(raw_smp_processor_id());
return sched_clock();
}
#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
@@ -340,12 +367,12 @@ u64 sched_clock_cpu(int cpu)
u64 cpu_clock(int cpu)
{
return sched_clock_cpu(cpu);
return sched_clock();
}
u64 local_clock(void)
{
return sched_clock_cpu(0);
return sched_clock();
}
#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */