linux-kernel - Re: [PATCH] Revert "genirq/affinity: assign vectors to all possible CPUs"

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Date:   Mon, 1 Oct 2018 17:59:48 +0200
From:   Paul Menzel <pmenzel+linux-scsi@...gen.mpg.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Ming Lei <ming.lei@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        it+linux-scsi@...gen.mpg.de,
        Adaptec OEM Raid Solutions <aacraid@...rosemi.com>,
        linux-scsi@...r.kernel.org,
        Raghava Aditya Renukunta 
        <RaghavaAditya.Renukunta@...rosemi.com>,
        Dave Carroll <david.carroll@...rosemi.com>
Subject: Re: [PATCH] Revert "genirq/affinity: assign vectors to all possible
 CPUs"

Dear Christoph,


On 10/01/18 14:43, Paul Menzel wrote:

> On 10/01/18 14:35, Christoph Hellwig wrote:
>> On Mon, Oct 01, 2018 at 02:33:07PM +0200, Paul Menzel wrote:
>>> Date: Wed, 29 Aug 2018 17:28:45 +0200
>>>
>>> This reverts commit ef86f3a72adb8a7931f67335560740a7ad696d1d.
>>
>> This seems rather odd.  If at all you'd revert the patch adding the
>> PCI_IRQ_AFFINITY to aacraid, not core infrastructure.
> 
> Thank you for the suggestion, but that flag was added in 2016
> to the aacraid driver.
> 
>> commit 0910d8bbdd99856af1394d3d8830955abdefee4a
>> Author: Hannes Reinecke <hare@...e.de>
>> Date:   Tue Nov 8 08:11:30 2016 +0100
>>
>>     scsi: aacraid: switch to pci_alloc_irq_vectors
>>     
>>     Use pci_alloc_irq_vectors and drop the hand-crafted interrupt affinity
>>     routines.
> 
> So what would happen, if `PCI_IRQ_AFFINITY` was removed? Will the
> system still work with the same performance?
> 
> As far as I understood, the no regression policy is there for
> exactly that reason, and it shouldn’t matter if it’s core
> infrastructure or not. As written, I have no idea, and just know
> reverting the commit in question fixes the problem here. So I’ll
> gladly test other solutions to fix this issue.

Just as another datapoint, with `PCI_IRQ_AFFINITY` removed from
`drivers/scsi/aacraid/comminit.c` in Linux 4.14.73, the driver
initializes correctly. I have no idea regarding the performance.


Kind regards,

Paul


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