linux-kernel - Re: [RFC PATCH 1/4] genirq: Provide basic NMI management for interrupt lines

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Date:   Wed, 18 Jul 2018 09:09:36 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        ricardo.neri-calderon@...ux.intel.com, marc.zyngier@....com,
        mingo@...nel.org
Subject: Re: [RFC PATCH 1/4] genirq: Provide basic NMI management for
 interrupt lines



On 17/07/18 20:46, Thomas Gleixner wrote:
> On Tue, 17 Jul 2018, Julien Thierry wrote:
>> On 17/07/18 16:51, Peter Zijlstra wrote:
>>> On Tue, Jul 17, 2018 at 04:48:17PM +0100, Julien Thierry wrote:
>>>> Supporting desc->affinity_hint for NMIs shouldn't be an issue, right?
>>>
>>> Shouldn't NMIs be strictly per cpu interrupt sources?
>>
>> That's a good question, and I don't have a proper answer right now...
>>
>> However, per cpu or not, the affinity still needs to be set for that
>> interrupt. It seemed to me that the desc->affinity_hint was just a way to keep
>> track of the interrupt affinity when it gets set through
>> irq_set_affinity_hint.
>>
>> Is that not the case?
> 
> No the affinity hint is a way to tell user space irqbalanced what the
> driver thinks is the best placement. Affinity settings are done by the
> kernel internal interfaces and those do not care about the hint at all.
> 

Oh, I see. Thanks for explaining

I already do set the IRQF_NOBALANCING for NMIs, so fiddling with that 
should be already limited.

I'll consider setting the IRQF_PERCPU (or mandating it for the NMI 
requests).

Thanks,

-- 
Julien Thierry