linux-kernel - Re: [PATCH 3/3] irq: Compute the periodic interval for interrupts

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Date:   Thu, 22 Jun 2017 17:25:56 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 3/3] irq: Compute the periodic interval for interrupts

On Tue, 20 Jun 2017, Daniel Lezcano wrote:
>  struct irq_timings {
>  	u64 values[IRQ_TIMINGS_SIZE]; /* our circular buffer */
> -	unsigned int count; /* Number of interruptions since last inspection */
> +	int count; /* Number of interruptions since last inspection */

WTF?

> +	ret = irq_timings_alloc(irq);
> +	if (ret) {
> +		pr_warn("Failed to allocate irq timing stats for irq%d (%d)",
> +			irq, ret);

That error code is -ENOMEM always, right?

> @@ -19,6 +25,18 @@ DEFINE_STATIC_KEY_FALSE(irq_timing_enabled);
>  
>  DEFINE_PER_CPU(struct irq_timings, irq_timings);
>  
> +struct irqt_stat {
> +	u64 ne;         /* next event                               */

Kernel doc format for struct documentation please. And with proper struct
member names you can spare that whole documentation.

What the heck is wrong with next_evt, last_ts, nr_samples or such ?

> +	u64 lts;	/* last timestamp                           */
> +	u64 variance;	/* variance                                 */
> +	u32 avg;	/* mean value                               */
> +	u32 count;      /* number of samples                        */
> +	int anomalies;  /* number of consecutives anomalies         */
> +	int valid;      /* behaviour of the interrupt               */
> +};

That would be too intuitive and spare a permanent lookup of the fricking
acronyms, right?

> +/**
> + * irqs_update - update the irq timing statistics with a new timestamp
> + *
> + * @irqs: an irqt_stat struct pointer
> + * @ts: the new timestamp
> + *
> + * ** This function must be called with the local irq disabled **

No need to yell here. And if you really fear that it's called with
interrupts enabled, then add a proper debug check.

Also instead of making mandatory statements it's better to explain WHY.

> +/**
> + * irq_timings_next_event - Return when the next event is supposed to arrive
> + *
> + * *** This function must be called with the local irq disabled ***

Idem.

> +void irq_timings_free(int irq)
> +{
> +	struct irqt_stat __percpu *s;
> +
> +	s = idr_find(&irqt_stats, irq);
> +	if (s) {
> +		free_percpu(s);
> +		idr_remove(&irqt_stats, irq);
> +	}
> +}
> +
> +int irq_timings_alloc(int irq)
> +{
> +	int id;
> +	struct irqt_stat __percpu *s;

	struct irqt_stat __percpu *s;
	int id;

Please ...

Don't bother to offer me a git tree, I'm going to apply that manually
anyway.

Thanks,

	tglx