linux-kernel - Re: [PATCH 01/12] genirq: Restrict effective affinity to single-target interrupts

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Message-ID: <83f8438b-0a4d-e11e-3c33-c7ebd6d7d1a0@arm.com>
Date:   Tue, 15 Aug 2017 13:18:50 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Wei Xu <xuwei5@...ilicon.com>,
        James Hogan <james.hogan@...tec.com>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Kevin Cernekee <cernekee@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Paul Burton <paul.burton@...tec.com>,
        Matt Redfearn <matt.redfearn@...tec.com>
Subject: Re: [PATCH 01/12] genirq: Restrict effective affinity to
 single-target interrupts

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...