linux-kernel - Re: [PATCH 3/3] nvme-pci: use queue close instead of queue freeze

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Date:   Sat, 8 Sep 2018 00:23:32 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org, jsmart2021@...il.com,
        sagi@...mberg.me, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, keith.busch@...el.com,
        jthumshirn@...e.de, bart.vanassche@....com
Subject: Re: [PATCH 3/3] nvme-pci: use queue close instead of queue freeze

On Thu, Sep 06, 2018 at 10:19:27PM +0800, jianchao.wang wrote:
> 
> 
> On 09/06/2018 09:07 PM, Ming Lei wrote:
> > On Thu, Sep 06, 2018 at 09:28:46AM +0800, jianchao.wang wrote:
> >> Hi Ming
> >>
> >> On 09/06/2018 06:09 AM, Ming Lei wrote:
> >>> nvme_dev_add() still may call freeze & unfreeze queue, so your patch
> >>> can't avoid draining queue completely here.
> >>
> >> Yes, I know this. We still need to freeze queue when update nr_hw_queues.
> >> But we move forward a step at least. :)
> >> We don't need to drain request queue in normal case of nvme_reset_work.
> > 
> > It is hard to say who is the normal case. In case of CPU hotplug, it is quite
> > easy to trigger updating nr_hw_queues.
> > 
> >>
> >> As for updating nr_hw_queues, we could try some other method on it next.
> > 
> > The thing is that draining queue may be inevitable inside reset work
> > function because of updating nr_hw_queues, that means the approach in
> > this patchset is just a partial solution
> > 
> > Or it may not make sense to do that because we may never remove the draining
> > queue in the code path of updating nr_hw_queues.
> > 
> > Given they belong to same issue, I suggest to solve them all.
> 
> I still think if just prevent new IO, freeze queue is over-kill.
> 
> With respect to update nr_hw_queues, we could try to take the bios down from the
> queued requests as the blk_steal_bios. Then re-issue these bios after updating the
> nr_hw_queues.

It is always easier to say than done, :-)

Please go ahead and post patches, and I am happy to review.


Thanks,
Ming