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sched/clock: Fixup early initialization 

The code would assume sched_clock_stable() and switch to !stable
later, this switch brings a discontinuity in time.

The discontinuity on switching from stable to unstable was always
present, but previously we would set stable/unstable before
initializing TSC and usually stick to the one we start out with.

So the static_key bits brought an extra switch where there previously
wasn't one.

Things are further complicated by the fact that we cannot use
static_key as early as we usually call set_sched_clock_stable().

Fix things by tracking the stable state in a regular variable and only
set the static_key to the right state on sched_clock_init(), which is
ran right after late_time_init->tsc_init().

Before this we would not be using the TSC anyway.

Reported-and-Tested-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: dyoung@redhat.com
Fixes: 35af99e646 ("sched/clock, x86: Use a static_key for sched_clock_stable")
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: paulmck@linux.vnet.ibm.com
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: rui.zhang@intel.com
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140122115918.GG3694@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Peter Zijlstra 2014-01-22 12:59:18 +01:00 committed by Ingo Molnar
parent 215393bc1f
commit d375b4e0fa
1 changed files with 41 additions and 12 deletions
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53
kernel/sched/clock.c
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@ -77,35 +77,50 @@ __read_mostly int sched_clock_running;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
static int __sched_clock_stable_early;
int sched_clock_stable(void)
{
if (static_key_false(&__sched_clock_stable))
return false;
return true;
return static_key_false(&__sched_clock_stable);
}
static void __set_sched_clock_stable(void)
{
if (!sched_clock_stable())
static_key_slow_inc(&__sched_clock_stable);
}
void set_sched_clock_stable(void)
{
if (!sched_clock_stable())
static_key_slow_dec(&__sched_clock_stable);
__sched_clock_stable_early = 1;
smp_mb(); /* matches sched_clock_init() */
if (!sched_clock_running)
return;
__set_sched_clock_stable();
}
static void __clear_sched_clock_stable(struct work_struct *work)
{
/* XXX worry about clock continuity */
if (sched_clock_stable())
static_key_slow_inc(&__sched_clock_stable);
static_key_slow_dec(&__sched_clock_stable);
}
static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
void clear_sched_clock_stable(void)
{
if (keventd_up())
schedule_work(&sched_clock_work);
else
__clear_sched_clock_stable(&sched_clock_work);
__sched_clock_stable_early = 0;
smp_mb(); /* matches sched_clock_init() */
if (!sched_clock_running)
return;
schedule_work(&sched_clock_work);
}
struct sched_clock_data {
@ -140,6 +155,20 @@ void sched_clock_init(void)
}
sched_clock_running = 1;
/*
* Ensure that it is impossible to not do a static_key update.
*
* Either {set,clear}_sched_clock_stable() must see sched_clock_running
* and do the update, or we must see their __sched_clock_stable_early
* and do the update, or both.
*/
smp_mb(); /* matches {set,clear}_sched_clock_stable() */
if (__sched_clock_stable_early)
__set_sched_clock_stable();
else
__clear_sched_clock_stable(NULL);
}
/*
@ -340,7 +369,7 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
*/
u64 cpu_clock(int cpu)
{
if (static_key_false(&__sched_clock_stable))
if (!sched_clock_stable())
return sched_clock_cpu(cpu);
return sched_clock();
@ -355,7 +384,7 @@ u64 cpu_clock(int cpu)
*/
u64 local_clock(void)
{
if (static_key_false(&__sched_clock_stable))
if (!sched_clock_stable())
return sched_clock_cpu(raw_smp_processor_id());
return sched_clock();