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

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Message-ID: <52C18CC3.9080507@redhat.com>
Date:	Mon, 30 Dec 2013 10:09:55 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	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 12/30/2013 02:44 AM, Chen, Gong wrote:
> 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.

Hmm ... okay.  I'll take a closer look at this.

Thanks for the additional information.

P.

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