linux-kernel - Re: [PATCH V8 2/3] irq: Track the interrupt timings

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Date:   Thu, 23 Mar 2017 15:14:22 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        peterz@...radead.org, rafael@...nel.org, vincent.guittot@...aro.org
Subject: Re: [PATCH V8 2/3] irq: Track the interrupt timings

On Thu, 23 Mar 2017, Daniel Lezcano wrote:

> +#define IRQ_TIMINGS_SHIFT	5
> +#define IRQ_TIMINGS_SIZE	(1 << IRQ_TIMINGS_SHIFT)
> +#define IRQ_TIMINGS_MASK	(IRQ_TIMINGS_SIZE - 1)
> +
> +struct irq_timing {
> +	u32 irq;
> +	u64 ts;
> +};
> +
> +struct irq_timings {
> +	struct irq_timing values[IRQ_TIMINGS_SIZE]; /* our circular buffer */

This is not very space efficient because of alignment restrictions from 
the u64 in struct irq_timing. 25% of the memory is wasted.

You could consider having two arrays instead:

	u32 irq_values[IRQ_TIMINGS_SIZE];
	u64 ts_values[IRQ_TIMINGS_SIZE];


Nicolas