netdev - Re: [PATCH net-next v11 2/5] netvsc: refactor notifier/event handling code to use the failover framework

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Date:   Wed, 23 May 2018 09:16:59 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, stephen@...workplumber.org,
        davem@...emloft.net, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org, jesse.brandeburg@...el.com,
        alexander.h.duyck@...el.com, kubakici@...pl, jasowang@...hat.com,
        loseweigh@...il.com, aaron.f.brown@...el.com,
        anjali.singhai@...el.com
Subject: Re: [PATCH net-next v11 2/5] netvsc: refactor notifier/event handling
 code to use the failover framework

On 5/22/2018 11:27 PM, Jiri Pirko wrote:
> Tue, May 22, 2018 at 10:54:29PM CEST, sridhar.samudrala@...el.com wrote:
>>
>> On 5/22/2018 9:12 AM, Jiri Pirko wrote:
>>> Fixing the subj, sorry about that.
>>>
>>> Tue, May 22, 2018 at 05:46:21PM CEST, mst@...hat.com wrote:
>>>> On Tue, May 22, 2018 at 05:36:14PM +0200, Jiri Pirko wrote:
>>>>> Tue, May 22, 2018 at 05:28:42PM CEST, sridhar.samudrala@...el.com wrote:
>>>>>> On 5/22/2018 2:08 AM, Jiri Pirko wrote:
>>>>>>> Tue, May 22, 2018 at 11:06:37AM CEST, jiri@...nulli.us wrote:
>>>>>>>> Tue, May 22, 2018 at 04:06:18AM CEST, sridhar.samudrala@...el.com wrote:
>>>>>>>>> Use the registration/notification framework supported by the generic
>>>>>>>>> failover infrastructure.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
>>>>>>>> In previous patchset versions, the common code did
>>>>>>>> netdev_rx_handler_register() and netdev_upper_dev_link() etc
>>>>>>>> (netvsc_vf_join()). Now, this is still done in netvsc. Why?
>>>>>>>>
>>>>>>>> This should be part of the common "failover" code.
>>>>>> Based on Stephen's feedback on earlier patches, i tried to minimize the changes to
>>>>>> netvsc and only commonize the notifier and the main event handler routine.
>>>>>> Another complication is that netvsc does part of registration in a delayed workqueue.
>>>>> :( This kind of degrades the whole efford of having single solution
>>>>> in "failover" module. I think that common parts, as
>>>>> netdev_rx_handler_register() and others certainly is should be inside
>>>>> the common module. This is not a good time to minimize changes. Let's do
>>>>> the thing properly and fix the netvsc mess now.
>>>>>
>>>>>
>>>>>> It should be possible to move some of the code from net_failover.c to generic
>>>>>> failover.c in future if Stephen is ok with it.
>>>>>>
>>>>>>
>>>>>>> Also note that in the current patchset you use IFF_FAILOVER flag for
>>>>>>> master, yet for the slave you use IFF_SLAVE. That is wrong.
>>>>>>> IFF_FAILOVER_SLAVE should be used.
>>>>>> Not sure which code you are referring to.  I only set IFF_FAILOVER_SLAVE
>>>>>> in patch 3.
>>>>> The existing netvsc driver.
>>>> We really can't change netvsc's flags now, even if it's interface is
>>>> messy, it's being used in the field. We can add a flag that makes netvsc
>>>> behave differently, and if this flag also allows enhanced functionality
>>>> userspace will gradually switch.
>>> Okay, although in this case, it really does not make much sense, so be
>>> it. Leave the netvsc set the ->priv flag to IFF_SLAVE as it is doing
>>> now. (This once-wrong-forever-wrong policy is flustrating me).
>>>
>>> But since this patchset introduces private flag IFF_FAILOVER and
>>> IFF_FAILOVER_SLAVE, and we set IFF_FAILOVER to the netvsc netdev
>>> instance, we should also set IFF_FAILOVER_SLAVE to the enslaved VF
>>> netdevice to get at least some consistency between virtio_net and
>>> netvsc.
>> OK. I can make this change to set/unset IFF_FAILOVER_SLAVE in the netvsc
>> register/unregister routines so that it is consistent with virtio_net.
>>
>> Based on your discussion with mst, i think we can even remove IFF_SLAVE
>> setting on netvsc as it should not impact userspace.  If Stephen is OK
>> we can make this change too.
>>
>> Do you see any other items that need to be resolved for this series to go in
>> this merge window?
> As I wrote previously, the common code including rx_handler registration
> and setting of flags and master link should be done in a common code,
> moved away from netvsc code.
>
This requires re-introducing the 2 additional ops pre_register and pre_unregister
that i removed in the last couple of revisions to minimize netvsc changes and the
indirect calls that Stephen expressed some concern.

But, as these calls don't happen in hot path, i guess it should not be a big
issue and the right way to go.
Will submit a v12 with these updates.