On Wed, 2012-07-11 at 14:45 +0200, Thomas Gleixner wrote:
> On Wed, 11 Jul 2012, Prarit Bhargava wrote:
> > On 07/10/2012 06:43 PM, John Stultz wrote:
> > > clock_was_set() cannot be called from hard interrupt context because
> > > it calls on_each_cpu(). For fixing the widely reported leap seconds
> > > issue it's necessary to call it from the timer interrupt context.
> > >
> > > Provide a new function which denotes it in the hrtimer cpu base
> > > structure of the cpu on which it is called and raising the timer
> > > softirq.
> > >
> > > We then execute the clock_was_set() notificiation in the timer softirq
> > > context in hrtimer_run_pending().
> >
> > I wish there was a nicer way to do this ... but looking at the code I can't
> > figure out a better way. (no offense John, it's just the way the code is
> > ;) )
>
> Yeah, I had the same discussion with Peter earlier today. There is
> only a rather limited set of options.
>
> 1) Retrigger the timer interrupt vectors on all CPUs - except the one
> we are running on, but we have no interface for that at the moment
>
> 2) Do the nasty __smp_call_function_single() hack
>
> Preallocate call_single_data for all cpus and do a
> __smp_call_function_single() on all online cpus.
>
> This can be called from hard interrupt context or irq disabled
> regions.
>
> That would allow to get rid of the whole delay magic all
> together.
>
> Thoughts?
The __smp_call_function_single() thing isn't particularly pretty either
and a lot more code to boot..
static DEFINE_PER_CPU(struct call_single_data, cws_csd);
void clock_was_set(void)
{
int cpu;
for_each_online_cpu(cpu) {
struct call_single_data *csd = &per_cpu(cws_csd, cpu);
if (csd->flags & CSD_FLAG_LOCK)
continue; /* a pending request is good enough */
csd->func = retrigger_next_event;
__smp_call_function_single(cpu, csd, 0);
}
timerfd_clock_was_set();
}
It also is a for_each_cpu loop with preemption disabled, not pretty :/
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