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Subject: Re: [PATCH 01/12] genirq: Restrict effective affinity to
 single-target interrupts
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Wei Xu <xuwei5@hisilicon.com>,
        James Hogan <james.hogan@imgtec.com>,
        Jason Cooper <jason@lakedaemon.net>, Andrew Lunn <andrew@lunn.ch>,
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        Kevin Cernekee <cernekee@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>,
        Paul Burton <paul.burton@imgtec.com>,
        Matt Redfearn <matt.redfearn@imgtec.com>
References: <20170815113447.14507-1-marc.zyngier@arm.com>
 <20170815113447.14507-2-marc.zyngier@arm.com>
 <alpine.DEB.2.20.1708151355390.1886@nanos>
From: Marc Zyngier <marc.zyngier@arm.com>
Organization: ARM Ltd
Message-ID: <83f8438b-0a4d-e11e-3c33-c7ebd6d7d1a0@arm.com>
Date: Tue, 15 Aug 2017 13:18:50 +0100
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On 15/08/17 13:01, Thomas Gleixner wrote:
> On Tue, 15 Aug 2017, Marc Zyngier wrote:
> 
>> Just because CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK is selected
>> doesn't mean that all the interrupts are using the effective
>> affinity mask. For a number of them, this mask is likely to
>> be empty.
>>
>> In order to deal with this, let's restrict the use of the
>> effective affinity mask to these interrupts that have been
>> configured as "single target".
> 
> That's actually wrong. On X86 we have other restrictions, i.e. groups of
> CPUs which are a subset of the affinity mask.

Ah, I completely missed that particular restriction.

> The point of the effective mask is to see to which CPU(s) a particular
> interrupt is effectively routed. This is always a subset of the affinity
> mask which is either the boot default or set by the admin.
> 
> So what you really want is to check whether the effective mask is
> empty. That's an indicator that the underlying irq chip does not update the
> effective mask.

Yes, that should do the trick. I'll update that patch.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...