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

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Date:	Sat, 9 Jan 2016 23:52:14 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Tom Herbert <tom@...bertland.com>
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 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.

Bye,
Hannes