[PATCH v14 24/25] sched: early boot clock

Pavel Tatashin
2018-07-18T02:22:10Z

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

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
init/main.c | 2 +-
kernel/sched/clock.c | 10 +++++++++-
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index 162d931c9511..ff0a24170b95 100644
--- a/init/main.c
+++ b/init/main.c
@@ -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();
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 0e9dbb2d9aea..7a8a63b940ee 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -202,7 +202,15 @@ static void __sched_clock_gtod_offset(void)

void __init sched_clock_init(void)
{
+ unsigned long flags;
+
sched_clock_running = 1;
+
+ /* Adjust __gtod_offset for contigious transition from early clock */
+ local_irq_save(flags);
+ sched_clock_tick();
+ local_irq_restore(flags);
+ __sched_clock_gtod_offset();
}
/*
* We run this as late_initcall() such that it runs after all built-in drivers,
@@ -356,7 +364,7 @@ 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);
--
2.18.0