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

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Message-ID: <b50cc2a3-bf3b-4f5a-97e6-dc2bfd29c99c@oracle.com>
Date:   Mon, 10 Sep 2018 09:49:41 +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 09/08/2018 12:23 AM, Ming Lei wrote:
> 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.
> 

Yes, I'm trying it and will post it when complete. :)

Thanks
Jianchao

> 
> Thanks,
> Ming
> 
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