[PATCH V4 1/2] nvme: add NVME_CTRL_RESET_PREPARE state

[jianchao.wang]

Hi James

Thanks for you detailed, kindly response and directive.
That's really appreciated.

On 01/18/2018 02:24 PM, James Smart wrote:
>> So in the patch, RESETTING in nvme-fc/rdma is changed to RESET_PREPARE. Then we get:
>> nvme-fc/rdma RESET_PREPARE -> RECONNECTING -> LIVE
>> nvme-pci     RESET_PREPARE -> RESETTING    -> LIVE
> 
> Right - so another way to look at this is you renamed RESETTING to RESET_PREPARE and added a new RESETTING state in the nvme-pci when in reinits.  Why not simply have the nvme-pci transport transition to RECONNECTING like the other transports. No new states, semantics are all the same.
> 
> Here's what the responsibility of the states are:
> RESETTING:
> -quiescing the blk-mq queues os errors don't bubble back to callees and new io is suspended
> -terminating the link-side association: resets the controller via register access/SET_PROPERTY, deletes connections/queues, cleans out active io and lets them queue for resending, etc.
> -end result is nvme block device is present, but idle, and no active controller on the link side  (link being a transport specific link such as pci, or ethernet/ib for rdma or fc link).
> 
> RECONNECTING:
> - "establish an association at the transport" on PCI this is immediate - you can either talk to the pci function or you can't. With rdma/fc we send transport traffic to create an admin q connection.
> - if association succeeded: the controller is init'd via register accesses/fabric GET/SET_PROPERTIES and admin-queue command, io connections/queues created, blk-mq queues unquiesced, and finally transition to NVME_CTRL_LIVE.
> - if association failed: check controller timeout., if not exceeded, schedule timer and retry later.  With pci, this could cover the temporary loss of the pci function access (a hot plug event) while keeping the nvme blk device live in the system.
> 
> It matches what you are describing but using what we already have in place - with the only difference being the addition of your "boundary" by adding the RECONNECTING state to nvme-pci.

Yes, absolutely. Thanks for your detailed summary here. 
Introducing RECONNECTING into nvme-pci is indeed a clearer way to fix the issue.

> 
> 
>>
>>>> I don't believe RESETTING and RECONNECTING are that similar - unless - you are looking at that "reinit" part that we left grandfathered into PCI.
>> Yes. I have got the point. Thanks for your directive.
>>
>> Both nvme-pc and nvme-fc/rdma have "shutdown" part to tear down queues/connects, quiesce queues, cancel outstanding requests...
>> We could call this part as "shutdowning" as well as the scheduling gap.
>> Because the difference of initializing between the nvme-pci and nvme-fc/rdma,  we could call "reiniting" for nvme-pci and
>> call "reconnecting" for nvme-fc/rdma
> 
> I don't think we need different states for the two. The actions taken are really very similar. How they do the actions varies slightly, but not what they are trying to do.   Thus, I'd prefer we keep the existing RECONNECTING state and use it in nvme-pci as well. I'm open to renaming it if there's something about the name that is not agreeable.

Yes. And I will use RECONNECTING in next version to fix this issue. If better name, could introduce in other patchset. :)


Many thanks again.
Jianchao