netdev - Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq

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Message-ID: <875z6w38n4.fsf@nanos.tec.linutronix.de>
Date:   Mon, 26 Oct 2020 23:49:35 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nitesh Narayan Lal <nitesh@...hat.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, helgaas@...nel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        frederic@...nel.org, sassmann@...hat.com,
        jesse.brandeburg@...el.com, lihong.yang@...el.com,
        jeffrey.t.kirsher@...el.com, jlelli@...hat.com, hch@...radead.org,
        bhelgaas@...gle.com, mike.marciniszyn@...el.com,
        dennis.dalessandro@...el.com, thomas.lendacky@....com,
        jiri@...dia.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, lgoncalv@...hat.com,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs

On Mon, Oct 26 2020 at 18:22, Nitesh Narayan Lal wrote:
> On 10/26/20 5:50 PM, Thomas Gleixner wrote:
>> But I still think that for curing that isolation stuff we want at least
>> some information from the driver. Alternative solution would be to grant
>> the allocation of interrupts and queues and have some sysfs knob to shut
>> down queues at runtime. If that shutdown results in releasing the queue
>> interrupt (via free_irq()) then the vector exhaustion problem goes away.
>
> I think this is close to what I and Marcelo were discussing earlier today
> privately.
>
> I don't think there is currently a way to control the enablement/disablement of
> interrupts from the userspace.

You cannot just disable the interrupt. You need to make sure that the
associated queue is shutdown or quiesced _before_ the interrupt is shut
down.

Thanks,

        tglx