linux-kernel - Re: [PATCH] x86: Add check for number of available vectors before CPU down [v2]

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Date:	Mon, 30 Dec 2013 02:44:34 -0500
From:	"Chen, Gong" <gong.chen@...ux.intel.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	rui wang <ruiv.wang@...il.com>, Tony Luck <tony.luck@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86-ML <x86@...nel.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Yang Zhang <yang.z.zhang@...el.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	janet.morgan@...el.com, "Yu, Fenghua" <fenghua.yu@...el.com>
Subject: Re: [PATCH] x86: Add check for number of available vectors before
 CPU down [v2]

On Sat, Dec 28, 2013 at 12:10:38PM -0500, Prarit Bhargava wrote:
> Gong and Rui,
> 
> After looking at this in detail I realized I made a mistake in my patch by
> including the check for the smp_affinity.  Simply put, it shouldn't be there
> given Rui's explanation above.
> 
> So I think the patch simply needs to do:
> 
>         this_count = 0;
>         for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
>                 irq = __this_cpu_read(vector_irq[vector]);
>                 if (irq >= 0) {
>                         desc = irq_to_desc(irq);
>                         data = irq_desc_get_irq_data(desc);
>                         affinity = data->affinity;
>                         if (irq_has_action(irq) && !irqd_is_per_cpu(data))
>                                 this_count++;
>                 }
>         }
> 
> Can the two of you confirm the above is correct?  It would be greatly appreciated.
> 

No, I don't think it is correct. We still need to consider smp_affinity.

fixup_irqs
        irq_set_affinity(native_ioapic_set_affinity)
                __ioapic_set_affinity
                        assign_irq_vector
                                __assign_irq_vector
                        cpu_mask_to_apicid_and
                /* now begin to set ioapic RET */

__assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
{
...
        apic->vector_allocation_domain(cpu, tmp_mask, mask);
...
        for_each_cpu_and(new_cpu, tmp_mask, cpu_online_mask)
                per_cpu(vector_irq, new_cpu)[vector] = irq;
        cfg->vector = vector;
        cpumask_copy(cfg->domain, tmp_mask);
...
}

On same vecotr on all related vector_irq, irq is set. So such kind of
irq should happen in multiple vector_irq. In cpu_mask_to_apicid_and(e.g.
x2apic_cpu_mask_to_apicid_and for cluster mode), apic is updated
depending on new mask. That's why I think this kind of interrupt
should be bypassed.

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