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

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Message-ID: <165989bc-949f-570e-c1d2-0ee1f0d4472a@oracle.com>
Date:   Thu, 6 Sep 2018 22:19:27 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, keith.busch@...el.com, jsmart2021@...il.com,
        sagi@...mberg.me, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        jthumshirn@...e.de, bart.vanassche@....com
Subject: Re: [PATCH 3/3] nvme-pci: use queue close instead of queue freeze



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.

Thanks
Jianchao

> 
> Thanks,
> Ming
> 
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