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

Peter Zijlstra
2018-07-19T10:39:03Z

On Tue, Jul 17, 2018 at 10:22:10PM -0400, Pavel Tatashin wrote:

> 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();

I think we want to keep __sched_clock_gtod_offset() inside the IRQ
disabled region.

And I just looked at my patch:

https://lkml.kernel.org/r/20180626090003.GA2458@hirez.programming.kicks-ass.net

and that had a comment about how we wanted to set the gtod offset
_before_ setting sched_clock_running, yet here you do it the other way
around. Hmm?

> }
> /*
> * 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);