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sched/clock: Enable sched clock early 

Allow sched_clock() to be used before schec_clock_init() is called.  This
provides a way to get early boot timestamps on machines with unstable
clocks.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: peterz@infradead.org
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-24-pasha.tatashin@oracle.com
This commit is contained in:
Pavel Tatashin 2018-07-19 16:55:42 -04:00 committed by Thomas Gleixner
parent 5d2a4e91a5
commit 857baa87b6
2 changed files with 20 additions and 2 deletions
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2
init/main.c
View File

@ -642,7 +642,6 @@ asmlinkage __visible void __init start_kernel(void)
softirq_init();
timekeeping_init();
time_init();
sched_clock_init();
printk_safe_init();
perf_event_init();
profile_init();
@ -697,6 +696,7 @@ asmlinkage __visible void __init start_kernel(void)
acpi_early_init();
if (late_time_init)
late_time_init();
sched_clock_init();
calibrate_delay();
pid_idr_init();
anon_vma_init();

20
kernel/sched/clock.c
View File

@ -202,7 +202,25 @@ static void __sched_clock_gtod_offset(void)
void __init sched_clock_init(void)
{
unsigned long flags;
/*
* Set __gtod_offset such that once we mark sched_clock_running,
* sched_clock_tick() continues where sched_clock() left off.
*
* Even if TSC is buggered, we're still UP at this point so it
* can't really be out of sync.
*/
local_irq_save(flags);
__sched_clock_gtod_offset();
local_irq_restore(flags);
sched_clock_running = 1;
/* Now that sched_clock_running is set adjust scd */
local_irq_save(flags);
sched_clock_tick();
local_irq_restore(flags);
}
/*
* We run this as late_initcall() such that it runs after all built-in drivers,
@ -356,7 +374,7 @@ u64 sched_clock_cpu(int cpu)
return sched_clock() + __sched_clock_offset;
if (unlikely(!sched_clock_running))
return 0ull;
return sched_clock();
preempt_disable_notrace();
scd = cpu_sdc(cpu);