Re: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

On Fri, 2020-06-12 at 17:29 +0200, Dario Faggioli wrote:
> On Fri, 2020-06-12 at 14:41 +0200, Jürgen Groß wrote:
> > On 12.06.20 14:29, Julien Grall wrote:
> > > On 12/06/2020 05:57, Jürgen Groß wrote:
> > > > On 12.06.20 02:22, Volodymyr Babchuk wrote:
> > > > > @@ -994,9 +998,22 @@ s_time_t sched_get_time_correction(struct 
> > > > > sched_unit *u)
> > > > >               break;
> > > > >       }
> > > > > +    spin_lock_irqsave(&sched_stat_lock, flags);
> > > > > +    sched_stat_irq_time += irq;
> > > > > +    sched_stat_hyp_time += hyp;
> > > > > +    spin_unlock_irqrestore(&sched_stat_lock, flags);
> > > > 
> > > > Please don't use a lock. Just use add_sized() instead which will
> > > > add
> > > > atomically.
> > > 
> > > If we expect sched_get_time_correction to be called concurrently
> > > then we 
> > > would need to introduce atomic64_t or a spin lock.
> > 
> > Or we could use percpu variables and add the cpu values up when
> > fetching the values.
> > 
> Yes, either percpu or atomic looks much better than locking, to me, for
> this.

Looks like we going to have atomic64_t after all. So, I'll prefer to to
use atomics there.