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

On 2021/6/24 16:10, Hannes Reinecke wrote:

On 6/24/21 9:29 AM, Chao Leng wrote:

quoted

On 2021/6/24 13:51, Hannes Reinecke wrote:

quoted

On 6/23/21 11:38 PM, Sagi Grimberg wrote:

quoted

quoted

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.

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.

Cheers,

Hannes

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