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

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Message-ID: <a5adee73-dde7-d00f-e7ef-1f81dc7c813a@amd.com>
Date:   Tue, 18 Sep 2018 23:09:57 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     David Miller <davem@...emloft.net>,
        "ahs3@...hat.com" <ahs3@...hat.com>
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 09/17/2018 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

>> -		enable_irq(ring->irq);
>> +		if (desc && desc->depth > 0)
>> +			enable_irq(ring->irq);
> 
> I really can't accept a patch that grovels into IRQ layer internals
> to work around a driver's IRQ enable/disable usage problem.
> 
> Sorry.
>