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Re: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.
- To: "dfaggioli@xxxxxxxx" <dfaggioli@xxxxxxxx>, "jgross@xxxxxxxx" <jgross@xxxxxxxx>, "julien@xxxxxxx" <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Fri, 12 Jun 2020 22:27:31 +0000
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- Delivery-date: Fri, 12 Jun 2020 22:27:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.
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.
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