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>
 <c32598b4-3f80-f83f-9b86-1c168752d1e2@gmail.com>
 <29258606-8255-847c-b22f-8793999ce6fe@gmail.com>
 <0e0f3aa6-9b6e-edd5-226f-2e23de9b5a0f@gmail.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <95391269-73b7-933f-27ee-2c4a17c8c6b1@gmail.com>
Date:   Tue, 18 Sep 2018 19:32:54 -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: <0e0f3aa6-9b6e-edd5-226f-2e23de9b5a0f@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 05:03 PM, Florian Fainelli wrote:
> On 09/18/2018 04:56 PM, Eric Dumazet wrote:
>>
>>
>> On 09/18/2018 04:27 PM, Eric Dumazet wrote:
>>>
>>
>>> I remember one of the napi_complete_done() change had to be reverted,
>>> for some obscure reason.
>>
>>
>>
>> That was not exactly a revert,  :
> 
> This is what I have so far for the drivers that both use
> napi_complete_done() without checking the return value and implement a
> ndo_poll_controller() callback:
> 
> https://github.com/ffainelli/linux/commits/napi-check

In fact, there is still to explain what the bug is.

napi_complete_done() return value can be ignored, unless drivers
have to disable IRQ in their interrupt handler, using the following
construct :

	if (napi_schedule_prep(napi)) {
               .... disable interrupt ....
               __napi_schedule_irqoff(napi);
        }

                 
It _can_ be used by other drivers to not rearm interrupts needlessly.

The bug discussed in this thread (re-balance IRQ usage) is of the same kind than
the one fixed in commit d7aba644ffdebf756e51e26a2229055211838e89 ("amd-xgbe: Enable IRQs only if napi_complete_done() is true")