nvme-tcp request timeouts

[Chaitanya Kulkarni]

On 10/11/22 13:14, Seth Forshee wrote:
> On Tue, Oct 11, 2022 at 07:30:56PM +0000, Chaitanya Kulkarni wrote:
>> Hi Seth,
>>
>> On 10/11/22 08:31, Seth Forshee wrote:
>>> Hi,
>>>
>>> I'm seeing timeouts like the following from nvme-tcp:
>>>
>>> [ 6369.513269] nvme nvme5: queue 102: timeout request 0x73 type 4
>>> [ 6369.513283] nvme nvme5: starting error recovery
>>> [ 6369.514379] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514385] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514392] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514393] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514401] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514414] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514420] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514427] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514430] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514432] block nvme5n1: no usable path - requeuing I/O
>>> [ 6369.514926] nvme nvme5: Reconnecting in 10 seconds...
>>> [ 6379.761015] nvme nvme5: creating 128 I/O queues.
>>> [ 6379.944389] nvme nvme5: mapped 128/0/0 default/read/poll queues.
>>> [ 6379.947922] nvme nvme5: Successfully reconnected (1 attempt)
>>>
>>> This is with 6.0, using nvmet-tcp on a different machine as the target.
>>> I've seen this sporadically with several test cases. The fio fio-rand-RW
>>> example test is a pretty good reproducer when numjobs in increased (I'm
>>> setting it equal to the number of CPUs in the system).
>>>
>>> Let me know what I can do to help debug this. I'm currently adding some
>>> tracing to the driver to see if I can get an idea of the sequence of
>>> events that leads to this problem.
>>>
>>> Thanks,
>>> Seth
>>>
>>
>> Can you bisect it ? that will help to understand the commit causing
>> issue.
> 
> I don't know of any "good" version right now. I started with a 5.10
> kernel and saw this, and tested 6.0 and still see it. I found several
> commits since 5.10 which fix some kind of timeouts:
> 
> a0fdd1418007 nvme-tcp: rerun io_work if req_list is not empty
> 70f437fb4395 nvme-tcp: fix io_work priority inversion
> 3770a42bb8ce nvme-tcp: fix regression that causes sporadic requests to time out
> 
> 5.10 still has timeouts with these backported, so whatever the problem
> is it has existed at least that long. I suppose I could go back to older
> kernels with these backported if that's going to be the best path
> forward here.
> 
> Thanks,
> Seth

Can you please share the fio config you are using ?

-ck