Messages in this thread Patch in this message | | | Date | Mon, 25 Jun 2018 10:55:43 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v12 10/11] sched: early boot clock |
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On Thu, Jun 21, 2018 at 05:25:17PM -0400, Pavel Tatashin wrote: > Allow sched_clock() to be used before schec_clock_init() and > sched_clock_init_late() are called. This provides us with a way to get > early boot timestamps on machines with unstable clocks.
There are !x86 architectures that use this code and might not expect to have their sched_clock() called quite that early. Please verify.
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> > --- > kernel/sched/clock.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c > index 10c83e73837a..f034392b0f6c 100644 > --- a/kernel/sched/clock.c > +++ b/kernel/sched/clock.c > @@ -205,6 +205,11 @@ void clear_sched_clock_stable(void) > */ > static int __init sched_clock_init_late(void) > { > + /* Transition to unstable clock from early clock */
This is wrong... or at least it smells horribly.
This is not the point where we transition from early to unstable, that is in fact in sched_clock_init.
This function, sched_clock_init_late(), is where we attempt to transition from unstable to stable. And this is _waaaay_ after SMP init.
> + local_irq_disable(); > + __gtod_offset = sched_clock() + __sched_clock_offset - ktime_get_ns(); > + local_irq_enable();
This might work in sched_clock_init(), which is pre-SMP.
> sched_clock_running = 2; > /* > * Ensure that it is impossible to not do a static_key update. > @@ -350,8 +355,9 @@ u64 sched_clock_cpu(int cpu) > if (sched_clock_stable()) > return sched_clock() + __sched_clock_offset; > > - if (unlikely(!sched_clock_running)) > - return 0ull; > + /* Use early clock until sched_clock_init_late() */ > + if (unlikely(sched_clock_running < 2)) > + return sched_clock() + __sched_clock_offset;
And then this remains !sched_clock_running, except instead of 0, you then return sched_clock() + __sched_clock_offset;
> preempt_disable_notrace(); > scd = cpu_sdc(cpu);
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