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Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping
 CPUs
To:     Thomas Gleixner <tglx@linutronix.de>,
        Nitesh Narayan Lal <nitesh@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>, helgaas@kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
        frederic@kernel.org, sassmann@redhat.com,
        jesse.brandeburg@intel.com, lihong.yang@intel.com,
        jeffrey.t.kirsher@intel.com, jlelli@redhat.com, hch@infradead.org,
        bhelgaas@google.com, mike.marciniszyn@intel.com,
        dennis.dalessandro@intel.com, thomas.lendacky@amd.com,
        jiri@nvidia.com, mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, lgoncalv@redhat.com,
        Jakub Kicinski <kuba@kernel.org>
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From:   Jacob Keller <jacob.e.keller@intel.com>
Organization: Intel Corporation
Message-ID: <586e249a-1078-9fe9-22d4-b3c1ec0a3a5e@intel.com>
Date:   Mon, 26 Oct 2020 16:08:08 -0700
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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