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sched/clock: Initialize all per-CPU state before switching (back) to unstable

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In preparation for not keeping the sched_clock_tick() active for
stable TSC, we need to explicitly initialize all per-CPU state
before switching back to unstable.

Note: this patch looses the __gtod_offset calculation; it will be
restored in the next one.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2017-04-21 12:11:53 +02:00 committed by Ingo Molnar
parent aa7b630ea0
commit cf15ca8ded
1 changed files with 39 additions and 21 deletions
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58
kernel/sched/clock.c
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@ -124,6 +124,12 @@ int sched_clock_stable(void)
return static_branch_likely(&__sched_clock_stable);
}
static void __scd_stamp(struct sched_clock_data *scd)
{
scd->tick_gtod = ktime_get_ns();
scd->tick_raw = sched_clock();
}
static void __set_sched_clock_stable(void)
{
struct sched_clock_data *scd = this_scd();
@ -141,8 +147,37 @@ static void __set_sched_clock_stable(void)
tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
}
/*
* If we ever get here, we're screwed, because we found out -- typically after
* the fact -- that TSC wasn't good. This means all our clocksources (including
* ktime) could have reported wrong values.
*
* What we do here is an attempt to fix up and continue sort of where we left
* off in a coherent manner.
*
* The only way to fully avoid random clock jumps is to boot with:
* "tsc=unstable".
*/
static void __sched_clock_work(struct work_struct *work)
{
struct sched_clock_data *scd;
int cpu;
/* take a current timestamp and set 'now' */
preempt_disable();
scd = this_scd();
__scd_stamp(scd);
scd->clock = scd->tick_gtod + __gtod_offset;
preempt_enable();
/* clone to all CPUs */
for_each_possible_cpu(cpu)
per_cpu(sched_clock_data, cpu) = *scd;
printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
scd->tick_gtod, __gtod_offset,
scd->tick_raw, __sched_clock_offset);
static_branch_disable(&__sched_clock_stable);
}
@ -150,26 +185,10 @@ static DECLARE_WORK(sched_clock_work, __sched_clock_work);
static void __clear_sched_clock_stable(void)
{
struct sched_clock_data *scd = this_scd();
/*
* Attempt to make the stable->unstable transition continuous.
*
* Trouble is, this is typically called from the TSC watchdog
* timer, which is late per definition. This means the tick
* values can already be screwy.
*
* Still do what we can.
*/
__gtod_offset = (scd->tick_raw + __sched_clock_offset) - (scd->tick_gtod);
printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
scd->tick_gtod, __gtod_offset,
scd->tick_raw, __sched_clock_offset);
if (!sched_clock_stable())
return;
tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
if (sched_clock_stable())
schedule_work(&sched_clock_work);
}
@ -357,8 +376,7 @@ void sched_clock_tick(void)
* XXX arguably we can skip this if we expose tsc_clocksource_reliable
*/
scd = this_scd();
scd->tick_raw = sched_clock();
scd->tick_gtod = ktime_get_ns();
__scd_stamp(scd);
if (!sched_clock_stable() && likely(sched_clock_running))
sched_clock_local(scd);