[PATCH v13 17/18] sched: early boot clock

[Pavel Tatashin]

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.tatas...@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 3b02be1fdfda..4d07b785d566 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -201,7 +201,15 @@ 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,
@@ -355,7 +363,7 @@ 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