netdev - Re: [PATCH net-next 0/4] net: switchdev: Avoid sleep in atomic with DSA

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Message-ID: <e28f29c8-04ed-1d71-7b13-27a5d58d111c@gmail.com>
Date:   Mon, 9 Jan 2017 12:56:48 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        vivien.didelot@...oirfairelinux.com, andrew@...n.ch,
        jiri@...nulli.us
Subject: Re: [PATCH net-next 0/4] net: switchdev: Avoid sleep in atomic with
 DSA

On 01/09/2017 12:48 PM, Ido Schimmel wrote:
> Hi Florian,
> 
> On Mon, Jan 09, 2017 at 11:44:59AM -0800, Florian Fainelli wrote:
>> Hi all,
>>
>> This patch series is to resolve a sleeping function called in atomic context
>> debug splat that we observe with DSA.
>>
>> Let me know what you think, I was also wondering if we should just always
>> make switchdev_port_vlan_fill() set SWITCHDEV_F_DEFER, but was afraid this
>> could cause invalid contexts to be used for rocker, mlxsw, i40e etc.
> 
> Isn't this a bit of overkill? All the drivers you mention fill the VLAN
> dump from their cache and don't require sleeping. Even b53 that you
> mention in the last patch does that, but reads the PVID from the device,
> which entails taking a mutex.

Correct.

> 
> Can't you just cache the PVID as well? I think this will solve your
> problem. Didn't look too much into the b53 code, so maybe I'm missing
> something. Seems that mv88e6xxx has a similar problem.

I suppose we could indeed cache the PVID for b53, but for mv88e6xxx it
seems like we need to perform a bunch of VTU operations, and those
access HW registers, Andrew, Vivien, how do you want to solve that, do
we want to introduce a general VLAN cache somewhere in switchdev/DSA/driver?

Thanks Ido!
-- 
Florian