netdev - Re: [PATCH net-next RFC 02/13] devlink: Add reload levels data to dev get

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Date:   Wed, 29 Jul 2020 14:11:17 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Moshe Shemesh <moshe@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Vasundhara Volam <vasundhara-v.volam@...adcom.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next RFC 02/13] devlink: Add reload levels data to
 dev get

On Wed, 29 Jul 2020 17:37:41 +0300 Moshe Shemesh wrote:
> > The fact that the driver supports fw_live_patch, does not necessarily
> > mean that the currently running FW can be live upgraded to the
> > currently flashed one, right?  
> 
> That's correct, though the feature is supported, the firmware gap may 
> not be suitable for live_patch.
> 
> The user will be noted accordingly by extack message.

That's kinda late, because use may have paid the cost of migrating the
workload or otherwise taking precautions - and if live reset fails all
this work is wasted.

While the device most likely knows upfront whether it can be live reset
or not, otherwise I don't see how it could reject the reset reliably.

> > This interface does not appear to be optimal for the purpose.
> >
> > Again, documentation of what can be lost (in terms of configuration and
> > features) upon upgrade is missing.  
> 
> I will clarify in documentation. On live_patch nothing should be lost or 
> re-initialized, that's the "live" thing.

Okay, so FW upgrade cannot be allowed when it'd mean the device gets
de-featured? Also no link loss, correct? What's the expected length of
traffic interruption (order of magnitude)?