netdev - Re: [PATCH net-next v4 06/10] netdev: add netdevice notifier type to trigger a reprogramming of offloads

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Date:	Mon, 11 Jan 2016 08:09:51 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Jesse Gross <jesse@...nel.org>
Subject: Re: [PATCH net-next v4 06/10] netdev: add netdevice notifier type to
 trigger a reprogramming of offloads

On Mon, Jan 11, 2016 at 4:11 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> On 10.01.2016 18:16, Tom Herbert wrote:
>>
>> On Sat, Jan 9, 2016 at 2:52 PM, Hannes Frederic Sowa <
>> hannes@...essinduktion.org> wrote:
>>>
>>> On 09.01.2016 23:27, Tom Herbert wrote:
>>>>
>>>>
>>>> On Sat, Jan 9, 2016 at 9:30 AM, Hannes Frederic Sowa
>>>> <hannes@...essinduktion.org> wrote:
>>>>>
>>>>>
>>>>> On 09.01.2016 18:25, Tom Herbert wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Sat, Jan 9, 2016 at 7:07 AM, Hannes Frederic Sowa
>>>>>> <hannes@...essinduktion.org> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
>>>>>>> ---
>>>>>>> include/linux/netdevice.h | 1 +
>>>>>>> 1 file changed, 1 insertion(+)
>>>>>>>
>>>>>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>>>>>> index 8d8e5ca951b493..9750e46760695d 100644
>>>>>>> --- a/include/linux/netdevice.h
>>>>>>> +++ b/include/linux/netdevice.h
>>>>>>> @@ -2183,6 +2183,7 @@ struct netdev_lag_lower_state_info {
>>>>>>> #define NETDEV_BONDING_INFO 0x0019
>>>>>>> #define NETDEV_PRECHANGEUPPER 0x001A
>>>>>>> #define NETDEV_CHANGELOWERSTATE 0x001B
>>>>>>> +#define NETDEV_REFRESH_OFFLOADS 0x001C
>>>>>>>
>>>>>> Per previous discussion we don't want to generalize this current
>>>>>> offload interface. Can we just NETDEV_UP as the notifier?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> The problem with only using NETDEV_UP/REGISTER is that some drivers
>>>>> need
>>>>> to
>>>>> reconfigure their offloads during operation while keeping the netdevice
>>>>> in
>>>>> UP state. One example is ixgbe. This was my first idea also.
>>>>>
>>>> It's configuration. Just get it once and save the port number(s) in
>>>> the driver. Configure the device only when
>>>> IXGBE_FLAG_VXLAN_OFFLOAD_CAPABLE is set.
>>>
>>>
>>>
>>> I don't see much value that each driver has to hold a database of ports
>>> to
>>> offload, the kernel knows much better and can easily be queried via this
>>> mechanism.
>>>
>>> This is not only about ixgbe, but also about benet, which f.e. needs the
>>> list of offloads available again during resume. Of course, drivers can do
>>> their own stateful handling of ports, but this seems to much more
>>> generate
>>> problems. I rather would like to see more logic moved into the core and
>>
>> less
>>>
>>> code in the drivers.
>>>
>> All the drivers that support VXLAN already save the ports in a stateful
>> fashion. Some support a single port, some and array, some a list. The only
>> question is whether they bother to save the information when the offload
>> feature is disabled. ixgbe does not for instance, but it looks like fm10k
>> does since it doesn't check any feature flags. Fixing those that don't
>> save
>> the information all the times should be straightforward.
>
>
> Yes, would probably be straight forward to add another list plus extra
> reference counting and maybe a lock, but I don't see why we need to
> duplicate the policy in the drivers? I personally think ixgbe does ok in
> this regard.
>
Again, to reiterate, _all_ the drivers that support VXLAN already save
the ports in a stateful fashion. Adding a new notifier is unnecessary
and makes things more complicated, not less. Also to reiterate, this
is not generic functionality that the driver is providing; we should
not need to add anything for this into the core APIs outside of the
two ndo functions that already exist.

Tom

> Anyway, this series merely tries to decouple 10gigbit cards from vxlan
> and/or geneve. It will be no problem to deal with this later on.
>
> Bye,
> Hannes
>