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

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Message-ID: <9594b4ee-f5bb-7d6e-f7e4-452091150dd6@redhat.com>
Date:   Tue, 18 Sep 2018 14:21:08 -0600
From:   Al Stone <ahs3@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        isubramanian@....com, kchudgar@....com, qnguyen@....com
Subject: Re: [PATCH] net: apm: xgene: force XGene enet driver to re-balance
 IRQ usage

On 09/17/2018 08:35 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);
>> -		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.

No worries.  I hesitated even sending it, actually.  The rewrite of the driver
that is needed is just something no one seems to have any interest in, or any
time for, but it really needs it to fix this properly (a colleague has found at
least one other issue in the structure of this driver, for example).  The cost
of doing that rewrite/restructure, though, far outweighs the benefit for this
device -- especially when the workaround is "don't run tuned".

I'll put a proper fix back on the list of Interesting Things to Work On When
Time Allows, for now.

Thanks for the quick -- and kind :) -- response.  I really appreciate it.

-- 
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3@...hat.com
-----------------------------------