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

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Message-ID: <95391269-73b7-933f-27ee-2c4a17c8c6b1@gmail.com>
Date:   Tue, 18 Sep 2018 19:32:54 -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 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")