netdev - Re: [PATCH net] ixgbe: check return value of napi_complete

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Date:   Fri, 21 Sep 2018 15:14:43 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Song Liu <songliubraving@...com>
CC:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        netdev <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH net] ixgbe: check return value of napi_complete_done()

On 9/21/18 7:59 AM, Eric Dumazet wrote:
>
>
> On 09/21/2018 07:55 AM, Alexei Starovoitov wrote:
>
>>
>> should we remove ndo_poll_controller then?
>> My understanding that the patch helps by not letting
>> drivers do napi_schedule() for all queues into this_cpu, right?
>> But most of the drivers do exactly that in their ndo_poll_controller
>> implementations. Means most of the drivers will experience
>> this nasty behavior.
>>
>
> Some legacy drivers do not use NAPI yet, but provide ndo_poll_controller()
>
> I believe users caring about system behavior with multi queue NIC are
> all using NAPI enabled drivers, so this should be fine.

I'm not following.
All modern napi enabled drivers need to _remove_ ndo_poll_controller
from the driver. This is a lot of churn.
Isn't it cleaner (less error prone) to introduce new ndo
for legacy drivers without napi?