Re: [PATCH v3 09/21] nvme: Implement cross-controller reset completion

[Hannes Reinecke <hare@suse.de>]

On 2/17/26 19:25, Mohamed Khalfella wrote:
> On Mon 2026-02-16 13:43:51 +0100, Hannes Reinecke wrote:
[ .. ]
>>
>> We really would need some indicator whether 'ccr' is supported at all.
> 
> Why do we need this indicator, other than exporting it via sysfs?
> 
To avoid false positives.

>> Using the number of available CCR commands would be an option, if though
>> that would require us to keep two counters (one for the number of
>> possible outstanding CCRs, and one for the number of actual outstanding
>> CCRs.).
> 
> Like mentioned above ctrl->ccr_limit gives us the number of ccrs
> available now. It is not 100% indicator if CCR is supported or not, but
> it is enough to implement CCR. A second counter can help us skip trying
> CCR if we know impacted controller does not support it.
> 
> Do you think it is worth it?
> 
Yes. The problem is that we want to get towards TP8028 compliance, which
forces us to wait for 2*KATO + CQT before requests on the failed patch
can be retried. That will cause a _noticeable_ stall on the application
side. And the only way to shorten that is CCR; once we get confirmation
from CCR we can start retrying immediately.
At the same time the current implementation only waits for 1*KATO before
retrying, so there will be regression if we switch to TP8028-compliant
KATO handling for systems not supporting CCR.

So we can (and should) use CCR as the determining factor whether we
want to switch to TP8028-compliant behaviour or stick with the original
implementation.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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