netdev - Re: [PATCH net-next RFC 01/13] devlink: Add reload level option to devlink reload command

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Message-ID: <20200728114458.762b5396@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 28 Jul 2020 11:44:58 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, Moshe Shemesh <moshe@...lanox.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Vasundhara Volam <vasundhara-v.volam@...adcom.com>
Subject: Re: [PATCH net-next RFC 01/13] devlink: Add reload level option to
 devlink reload command

On Tue, 28 Jul 2020 09:47:00 -0700 Jacob Keller wrote:
> On 7/28/2020 6:58 AM, Jiri Pirko wrote:
> > But this is needed to maintain the existing behaviour which is different
> > for different drivers.
> 
> Which drivers behave differently here?

I think Jiri refers to mlxsw vs mlx5.

mlxsw loads firmware on probe, by default at least. So reloading the
driver implies a FW reset. NIC drivers OTOH don't generally load FW
so they didn't reset FW.

Now since we're redefining the API from "do a reload so that driverinit
params are applied" (or "so that all netdevs get spawned in a new
netns") to "do a reset of depth X" we have to change the paradigm.

What I was trying to suggest is that we should not have to re-define
the API like this.

From user perspective what's important is what the reset achieves (and
perhaps how destructive it is). We can define the reset levels as:

$ devlink dev reload pci/0000:82:00.0 net-ns-respawn
$ devlink dev reload pci/0000:82:00.0 driver-param-init
$ devlink dev reload pci/0000:82:00.0 fw-activate

combining should be possible when user wants multiple things to happen:

$ devlink dev reload pci/0000:82:00.0 fw-activate driver-param-init

Then we have the use case of a "live reset" which is slightly
under-defined right now IMHO, but we can extend it as:

$ devlink dev reload pci/0000:82:00.0 fw-activate --live

We can also add the "reset level" specifier - for the cases where
device is misbehaving:

$ devlink dev reload pci/0000:82:00.0 level [driver|fw|hardware]

But I don't think that we can go from the current reload command
cleanly to just a level reset. The driver-specific default is a bad
smell which indicates we're changing semantics from what user wants 
to what the reset depth is. Our semantics with the patch as it stands
are in fact:
 - if you want to load new params or change netns, don't pass the level
   - the "driver default" workaround dictates the right reset level for
   param init;
 - if you want to activate new firmware - select the reset level you'd
   like from the reset level options.