RE: [PATCH V5 1/5] scsi: hpsa: fix selection of reply queue

[Kashyap Desai <kashyap.desai@broadcom.com>]

> -----Original Message-----
> From: Artem Bityutskiy [mailto:dedekind1@gmail.com]
> Sent: Monday, March 19, 2018 8:12 PM
> To: hch@lst.de; Thomas Gleixner
> Cc: linux-block@vger.kernel.org; snitzer@redhat.com; hare@suse.de;
> mroos@linux.ee; linux-scsi@vger.kernel.org; don.brace@microsemi.com;
> pbonzini@redhat.com; loberman@redhat.com;
> kashyap.desai@broadcom.com; Jens Axboe; martin.petersen@oracle.com;
> James.Bottomley@HansenPartnership.com; ming.lei@redhat.com
> Subject: Re: [PATCH V5 1/5] scsi: hpsa: fix selection of reply queue
>
> On Mon, 2018-03-19 at 08:31 -0600, Jens Axboe wrote:
> > I'm assuming that Martin will eventually queue this up. But probably
> > for 4.17, then we can always flag it for a backport to stable once
> > it's been thoroughly tested.
>
> Jens, thanks for reply.
>
> I wonder if folks agree that in this case we should revert
>
> 84676c1f21e8 genirq/affinity: assign vectors to all possible CPUs
>
> for v4.16.
>
> If this was a minor niche use-case regression the -stable scenario would
> probably be OK. But the patch seem to miss the fact that kernel's
> "possible
> CPUs" notion may be way off and side effects are bad.

Also it is performance issue as posted at below link, if we just use
"84676c1f21e8 genirq/affinity: assign vectors to all possible CPUs".

https://www.spinics.net/lists/linux-scsi/msg118301.html

Performance drop was resolved using patch set (available at below link)under
discussion posted by Ming.

https://marc.info/?l=linux-block&m=152050646332092&w=2

Kashyap

>
> Christoph, Thomas, what do you think?
>
> Thanks,
> Artem.