Re: [PATCH v5 07/10] sched/irq: add irq utilization tracking

[Dietmar Eggemann]

On 06/07/2018 10:44 AM, Vincent Guittot wrote:
> On 7 June 2018 at 10:29, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> > On 06/06/2018 06:06 PM, Vincent Guittot wrote:
> > > Hi Dietmar,
> > >
> > > Sorry for the late answer
> > >
> > > On 31 May 2018 at 18:54, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> > > wrote:
> > > > On 05/30/2018 08:45 PM, Vincent Guittot wrote:
> > > > > Hi Dietmar,
> > > > >
> > > > > On 30 May 2018 at 17:55, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> > > > > wrote:
> > > > > > On 05/25/2018 03:12 PM, Vincent Guittot wrote:

[...]

> > Can't buy this argument though because this is true with the current
> > implementation as well since the 'decay load sum' - 'accrue load sum'
> > sequence is not atomic.
>
> it's not a problem that the _sum variable are updated in different
> step because there are internal variable
> Only util_avg is used "outside" and the latter is updated after both
> idle and running steps have been applied

You're right here!

> > What about calling update_irq_load_avg(rq, 0) in update_rq_clock_task() if
> > (irq_delta + steal) eq. 0 and sched_feat(NONTASK_CAPACITY) eq. true in this
> > #ifdef CONFIG_XXX_TIME_ACCOUNTING block?
>
> update_irq_load_avg(rq, 0) is called in update_blocked_averages to
> decay smoothly like other blocked signals and replace the need to call
> update_irq_load_avg(rq, 0) for every call to update_rq_clock_task()
> which can be significant

OK.

> > Maintaining a irq/steal time signal makes only sense if at least one of the
> > CONFIG_XXX_TIME_ACCOUNTING is set and NONTASK_CAPACITY is true. The call to
> > update_irq_load_avg() in update_blocked_averages() isn't guarded my them.
>
> good point

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