linux-kernel - Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

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Message-ID: <56A0A454.7020606@linaro.org>
Date:	Thu, 21 Jan 2016 10:26:44 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	tglx@...utronix.de, rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, nicolas.pitre@...aro.org,
	vincent.guittot@...aro.org
Subject: Re: [RFC V2 1/2] irq: Add a framework to measure interrupt timings

On 01/20/2016 08:07 PM, Peter Zijlstra wrote:
> On Wed, Jan 20, 2016 at 05:00:32PM +0100, Daniel Lezcano wrote:
>> +++ b/kernel/irq/handle.c
>> @@ -165,6 +165,7 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
>>   			/* Fall through to add to randomness */
>>   		case IRQ_HANDLED:
>>   			flags |= action->flags;
>> +			handle_irqtiming(irq, action->dev_id);
>>   			break;
>>
>>   		default:
>
>> +++ b/kernel/irq/internals.h
>
>> +static inline void handle_irqtiming(unsigned int irq, void *dev_id)
>> +{
>> +	if (__irqtimings->handler)
>> +		__irqtimings->handler(irq, ktime_get(), dev_id);
>> +}
>
> Here too, ktime_get() is daft.
>
> Also, you really want to take the timestamp _before_ we call the
> handlers, not after, otherwise you mix in whatever variance exist in the
> handler duration.

Indeed.



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