linux-kernel - Re: [PATCH V5] irq: Track the interrupt timings

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Date:	Tue, 14 Jun 2016 13:46:34 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	tglx@...utronix.de, shreyas@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	rafael@...nel.org, vincent.guittot@...aro.org
Subject: Re: [PATCH V5] irq: Track the interrupt timings

On Tue, 14 Jun 2016, Daniel Lezcano wrote:

[...]

> +void __handle_timings(struct irq_desc *desc)
> +{
> +	struct irq_timings *timings;
> +	u64 prev, now, diff;
> +
> +	timings = this_cpu_ptr(desc->timings);
> +	now = local_clock();
> +	prev = timings->timestamp;
> +	timings->timestamp = now;
> +
> +	/*
> +	 * In case it is the first time this function is called, the
> +	 * 'prev' variable will be zero which reflects the time origin
> +	 * when the system booted.
> +	 */
> +	diff = now - prev;
> +
> +	/* The oldest value corresponds to the next index. */
> +	timings->w_index = (timings->w_index + 1) & IRQ_TIMINGS_MASK;
> +	timings->values[timings->w_index] = diff;
> +}

What about simply this:

void __handle_timings(struct irq_desc *desc)
{
	struct irq_timings *timings = this_cpu_ptr(desc->timings);
	timings->w_index = (timings->w_index + 1) & IRQ_TIMINGS_MASK;
	timings->values[timings->w_index] = local_clock();
}

?

Then you could s/__handle_timings/__record_irq_time/ to better represent 
what it does.  And both the difference and the summing of squares could 
be done upon entering idle instead.


Nicolas