linux-kernel - Re: [PATCH V7] irq: Track the interrupt timings

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Message-ID: <576BE039.9060703@linaro.org>
Date:	Thu, 23 Jun 2016 15:12:25 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	nicolas.pitre@...aro.org, shreyas@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	rafael@...nel.org, vincent.guittot@...aro.org
Subject: Re: [PATCH V7] irq: Track the interrupt timings

On 06/23/2016 12:12 PM, Thomas Gleixner wrote:
> On Thu, 23 Jun 2016, Daniel Lezcano wrote:
>> On 06/23/2016 10:41 AM, Thomas Gleixner wrote:
>>> Is it really required to do this per interrupt rather than providing per cpu
>>> statistics of interrupts which arrived in the last X seconds or whatever
>>> timeframe is relevant for this.
>>
>> Perhaps I am misunderstanding but if the statistics are done per cpu without
>> tracking per irq timings, it is not possible to extract a repeating pattern
>> for each irq and have an accurate prediction.
>
> I don't see why you need a repeating pattern for each irq. All you want to
> know is whether there are repeating patterns of interrupts on a particular
> cpu.
>
> struct per_cpu_stat {
>         u32	    irq;
>         u64	    ts;
> };
>
> storing 32 entries of the above should give you enough information about
> patterns etc. If you have a high rate of interrupts on that cpu it does not
> matter at all whether thats from one or several devices. If you have only a
> few then this storage is sufficient to get the desired information.

Mmmh, yes. I will investigate this patchset by replacing the percpu 
irqdesc's timings field by a per cpu irq event timings array.

Thanks !

   -- Daniel


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