netdev - Re: [PATCH] net: apm: xgene: force XGene enet driver to re-balance IRQ usage

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Message-ID: <c32598b4-3f80-f83f-9b86-1c168752d1e2@gmail.com>
Date:   Tue, 18 Sep 2018 16:27:28 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>, ahs3@...hat.com,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "isubramanian@....com" <isubramanian@....com>,
        "kchudgar@....com" <kchudgar@....com>,
        "qnguyen@....com" <qnguyen@....com>
Subject: Re: [PATCH] net: apm: xgene: force XGene enet driver to re-balance
 IRQ usage



On 09/18/2018 04:21 PM, Florian Fainelli wrote:
> On 09/18/2018 04:15 PM, Al Stone wrote:
>> On 09/18/2018 05:09 PM, Lendacky, Thomas wrote:
>>>
>>>
>>> On 09/17/2018 09:35 PM, David Miller wrote:
>>>> From: Al Stone <ahs3@...hat.com>
>>>> Date: Mon, 17 Sep 2018 17:35:33 -0600
>>>>
>>>>> @@ -866,8 +866,11 @@ static int xgene_enet_napi(struct napi_struct *napi, const int budget)
>>>>>  	processed = xgene_enet_process_ring(ring, budget);
>>>>>  
>>>>>  	if (processed != budget) {
>>>>> +		struct irq_desc *desc = irq_to_desc(ring->irq);
>>>>> +
>>>>>  		napi_complete_done(napi, processed);
>>>
>>> The problem could be that the driver isn't checking the
>>> napi_complete_done() return code.  It was changed to return a bool and
>>> the check should be more like:
>>>
>>>   if ((processed != budget) && napi_complete_done(napi, processed)) {
>>>
>>> If it returns false, then the driver will get called for polling again
>>> after having issued enable_irq() and it well then issue the enable_irq()
>>> a second (or more) time without having the matching diable_irq().
>>>
>>> Thanks,
>>> Tom
>>
>> Aha, that might be.  My apologies -- I play in ACPI but seldom in the network
>> drivers, so was not fully aware of that change.  I can give that a try.
>>
>> Thanks for the pointer.
> 
> FWIW this is being discussed in this thread as well:
> 
> https://www.spinics.net/lists/netdev/msg523760.html
> 
> there should be an update to drivers that have a ndo_poll_controller()
> and don't check napi_complete_done(), though I am not clear who is doing
> that yet.

That might be tricky.

I remember one of the napi_complete_done() change had to be reverted,
for some obscure reason.

So clearly, doing a mass update (without being able to test the driver on real hardware) might be risky.