linux-kernel - Re: [PATCH linux-next v3 1/2] irq: Add CPU mask affinity hint

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Date:	Fri, 30 Apr 2010 14:18:29 -0700 (Pacific Daylight Time)
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Ben Hutchings <bhutchings@...arflare.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"arjan@...ux.jf.intel.com" <arjan@...ux.jf.intel.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH linux-next v3 1/2] irq: Add CPU mask affinity hint

On Fri, 30 Apr 2010, Thomas Gleixner wrote:

> On Fri, 30 Apr 2010, Ben Hutchings wrote:
>> On Fri, 2010-04-30 at 13:23 -0700, Peter P Waskiewicz Jr wrote:
>>> +int irq_register_affinity_hint(unsigned int irq, const struct cpumask *m)
>>> +{
>>> +	struct irq_desc *desc = irq_to_desc(irq);
>>> +	unsigned long flags;
>>> +
>>> +	if (!desc)
>>> +		return -EINVAL;
>>
>> Is it possible for irq_to_desc(irq) to be NULL?  This function already
>> assumes that the caller 'owns' the IRQ.
>
> Oh come on. Driver writers get everything wrong and not checking on an
> invalid irq number is better than crashing :)
>
>>> +static int irq_affinity_hint_proc_show(struct seq_file *m, void *v)
>>> +{
>>> +	struct irq_desc *desc = irq_to_desc((long)m->private);
>>> +	unsigned long flags;
>>> +	cpumask_var_t mask;
>>> +	int ret = -EINVAL;
>>
>> I don't think this should be returning -EINVAL if the affinity hint is
>> missing.  That means 'invalid argument', but there is nothing invalid
>> about trying to read() the corresponding file.  The file should simply
>> be empty if there is no hint.  (Actually it might be better if it didn't
>> appear at all, but that would be a pain to implement.)
>
> I agree that -EINVAL is not really a good match.
>
> How about just returning CPU_MASK_ALL if desc->affinity_hint is not
> set ?

That seems reasonable to me.

cheers,
-PJ
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