Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] net: apm: xgene: force XGene enet driver to re-balance
 IRQ usage
To:     Florian Fainelli <f.fainelli@gmail.com>, ahs3@redhat.com,
        "Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
        David Miller <davem@davemloft.net>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "isubramanian@apm.com" <isubramanian@apm.com>,
        "kchudgar@apm.com" <kchudgar@apm.com>,
        "qnguyen@apm.com" <qnguyen@apm.com>
References: <20180917233533.28626-1-ahs3@redhat.com>
 <20180917.193531.1424852853827678152.davem@davemloft.net>
 <a5adee73-dde7-d00f-e7ef-1f81dc7c813a@amd.com>
 <4929e93d-508a-4670-9450-66e4fc85be7e@redhat.com>
 <cdb8a00c-a3bf-72e0-38b2-3c4b2427270a@gmail.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <c32598b4-3f80-f83f-9b86-1c168752d1e2@gmail.com>
Date:   Tue, 18 Sep 2018 16:27:28 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <cdb8a00c-a3bf-72e0-38b2-3c4b2427270a@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


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@redhat.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.