Re: [LSF/MM/BPF BOF] Userspace command abouts

[Hannes Reinecke <hare@suse.de>]

On 2/25/23 02:51, Keith Busch wrote:
> On Fri, Feb 24, 2023 at 11:54:39PM +0000, Chaitanya Kulkarni wrote:
>> I do think that we should work on CDL for NVMe as it will solve some of
>> the timeout related problems effectively than using aborts or any other
>> mechanism.
> 
> That proposal exists in NVMe TWG, but doesn't appear to have recent activity.
> The last I heard, one point of contention was where the duration limit property
> exists: within the command, or the queue. From my perspective, if it's not at
> the queue level, the limit becomes meaningless, but hey, it's not up to me.

And that is one of the issues I'd like to discuss.
As it stands CDL are defined for the controller only, queuing effects 
from the transport are out of scope (for the current CDL definition).
So for NVMe-oF we would need to discuss how we can specify CDLs for 
fabrics; especially the relationship between CDLs and transport timeouts 
are ... interesting, and we need to discuss how we can correlate both.

Having it on the queue as you suggested would be cool as it would give a 
nice overall number, but discussions with the driver vendors were not 
encouraging; they're having a hard time giving timeout guarantees in 
really quirky failure cases.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew
Myers, Andrew McDonald, Martje Boudien Moerman