[PATCH 0/2] nvme-fabrics: short-circuit connect retries

[Hannes Reinecke]

On 6/26/21 3:03 AM, Chao Leng wrote:
> 
> 
> On 2021/6/24 16:10, Hannes Reinecke wrote:
>> On 6/24/21 9:29 AM, Chao Leng wrote:
>>>
>>>
>>> On 2021/6/24 13:51, Hannes Reinecke wrote:
>>>> On 6/23/21 11:38 PM, Sagi Grimberg wrote:
>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> commit f25f8ef70ce2 ("nvme-fc: short-circuit reconnect retries")
>>>>>> allowed the fc transport to honour the DNR bit during reconnect
>>>>>> retries, allowing to speed up error recovery.
>>>>>
>>>>> How does this speed up error recovery?
>>>>
>>>> Well, not exactly error recovery (as there is nothing to recover).
>>>> But we won't attempt pointless retries, thereby reducing the noise in
>>>> the message log.
>>> This conflict with the tcp and rdma target.
>>> You may need to delete the improper NVME_SC_DNR at the target.
>>> However, this will cause compatibility issues between different 
>>> versions.
>>
>> Which ones?
> In many scenarios, the destination sets DNR for abnormal packets,
> but each new connection may not have the same error.

This patch series is only for the DNR bit set in response to the 
'connect' command.
If the target is not able to process the 'connect' command, but may be 
so in the future it really should not set the DNR bit.

>> I checked the DNR usage in the target code, and they seem to set it
>> correctly (ie the result would not change when the command is retried).
>> With the possible exception of ENOSPC handling, as this is arguably
>> dynamic and might change with a retry.
> The DNR status of the old connection may not be relevant to the 
> re-established connection.

See above.
We are just checking the DNR settings for the 'connect' command (or any 
other commands being sent during initial controller configuration).
If that fails the connect never was properly initialized; if the 
controller would return a different status after reconnect it simply 
should not set the DNR bit ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare at suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer