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

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Message-ID: <20180906130715.GB31250@ming.t460p>
Date:   Thu, 6 Sep 2018 21:07:16 +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 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.

Thanks,
Ming