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

Dietmar Eggemann
2018-06-07T08:29:26Z

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@arm.com> wrote:
>> On 05/30/2018 08:45 PM, Vincent Guittot wrote:
>>> Hi Dietmar,
>>>
>>> On 30 May 2018 at 17:55, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>> On 05/25/2018 03:12 PM, Vincent Guittot wrote:
>>
>> [...]
>>
>>>>> + */
>>>>> + ret = ___update_load_sum(rq->clock - running, rq->cpu,
>>>>> &rq->avg_irq,
>>>>> + 0,
>>>>> + 0,
>>>>> + 0);
>>>>> + ret += ___update_load_sum(rq->clock, rq->cpu, &rq->avg_irq,
>>>>> + 1,
>>>>> + 1,
>>>>> + 1);
>>
>> Can you not change the function parameter list to the usual
>> (u64 now, struct rq *rq, int running)?
>>
>> Something like this (only compile and boot tested):
>
> To be honest, I prefer to keep the specific sequence above in a
> dedicated function instead of adding it in core code.

No big issue.

> Furthermore, we end up calling call twice ___update_load_avg instead
> of only once. This will set an intermediate and incorrect value in
> util_avg and this value can be read in the meantime

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.

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?

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. …