linux-kernel - Re: [Patch v2] x86, irq: Support CPU vector allocation policies

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Date:	Wed, 6 May 2015 12:22:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>, x86@...nel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
	Daniel J Blueman <daniel@...ascale.com>
Subject: Re: [Patch v2] x86, irq: Support CPU vector allocation policies

On Wed, 6 May 2015, Jiang Liu wrote:
> Hi Thomas,
> 	This is the simplified version, which removed the kernel parameter.
> Seems much simpler:)

But it can be made even simpler. :)
 
> +enum {
> +	/* Allocate CPU vectors from CPUs on device local node */
> +	X86_VECTOR_POL_NODE = 0x1,
> +	/* Allocate CPU vectors from all online CPUs */
> +	X86_VECTOR_POL_GLOBAL = 0x2,
> +	/* Allocate CPU vectors from caller specified CPUs */
> +	X86_VECTOR_POL_CALLER = 0x4,
> +	X86_VECTOR_POL_MIN = X86_VECTOR_POL_NODE,
> +	X86_VECTOR_POL_MAX = X86_VECTOR_POL_CALLER,
> +};

  
> +static int assign_irq_vector_policy(int irq, int node,
> +				    struct apic_chip_data *data,
> +				    struct irq_alloc_info *info)
> +{
> +	int err = -EBUSY;
> +	unsigned int policy;
> +	const struct cpumask *mask;
> +
> +	if (info && info->mask)
> +		policy = X86_VECTOR_POL_CALLER;
> +	else
> +		policy = X86_VECTOR_POL_MIN;
> +
> +	for (; policy <= X86_VECTOR_POL_MAX; policy <<= 1) {
> +		switch (policy) {
> +		case X86_VECTOR_POL_NODE:
> +			if (node >= 0)
> +				mask = cpumask_of_node(node);
> +			else
> +				mask = NULL;
> +			break;
> +		case X86_VECTOR_POL_GLOBAL:
> +			mask = apic->target_cpus();
> +			break;
> +		case X86_VECTOR_POL_CALLER:
> +			if (info && info->mask)
> +				mask = info->mask;
> +			else
> +				mask = NULL;
> +			break;
> +		default:
> +			mask = NULL;
> +			break;
> +		}
> +		if (mask) {
> +			err = assign_irq_vector(irq, data, mask);
> +			if (!err)
> +				return 0;
> +		}
> +	}

This looks pretty overengineered now that you don't have that parameter check.

	if (info && info->mask)
		return assign_irq_vector(irq, data, info->mask);

	if (node >= 0) {
		err = assign_irq_vector(irq, data, cpumask_of_node(node));
		if (!err)
			return 0;
	}

	return assign_irq_vector(irq, data, apic->target_cpus());

Should do the same, right?

Thanks,

	tglx
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