linux-kernel - Re: Affinity managed interrupts vs non-managed interrupts

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Message-ID: <20180911091354.GA9898@lst.de>
Date:   Tue, 11 Sep 2018 11:13:54 +0200
From:   Christoph Hellwig <hch@....de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dou Liyang <dou_liyang@....com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Ming Lei <tom.leiming@...il.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shivasharan Srikanteshwara 
        <shivasharan.srikanteshwara@...adcom.com>,
        linux-block <linux-block@...r.kernel.org>,
        Dou Liyang <douly.fnst@...fujitsu.com>
Subject: Re: Affinity managed interrupts vs non-managed interrupts

On Thu, Sep 06, 2018 at 01:46:46PM +0200, Thomas Gleixner wrote:
> There are a few things we need to clarify upfront:
> 
> Right now the pre and post vectors are marked managed and their
> affinity mask is set to the irq default affinity mask.
> 
> The default affinity mask is by default ALL cpus, but it can be tweaked
> both on the kernel command line and via proc.
> 
> If that mask is only a subset of CPUs and all of them go offline
> then these vectors are shutdown in managed mode.
> 
> That means we need to set the affinity mask of the pre and post vectors to
> possible mask, but that doesn't make much sense either, unless there is a
> reason to have them marked managed.
> 
> I think the right solution for these pre/post vectors is to _NOT_ mark
> them managed and leave them as regular interrupts which can be affinity
> controlled and also can move freely on hotplug.

Yes, agreed.  Marking the pre/post vector as managed was a mistake
(and I don't think it even was intentional, at least on my part).