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

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Message-ID: <586e249a-1078-9fe9-22d4-b3c1ec0a3a5e@intel.com>
Date:   Mon, 26 Oct 2020 16:08:08 -0700
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Nitesh Narayan Lal <nitesh@...hat.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 10/26/2020 3:49 PM, Thomas Gleixner wrote:
> 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
> 

Could this be handled with a callback to the driver/hw? I know Intel HW
should support this type of quiesce/shutdown.

Thanks,
Jake