linux-kernel - Re: [PATCH] x86 - irq vector assignment

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Date:	Tue, 21 Sep 2010 23:34:17 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Jack Steiner <steiner@....com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86 - irq vector assignment

On Tue, 21 Sep 2010, Yinghai Lu wrote:
> >  arch/x86/kernel/apic/io_apic.c |    5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > Index: linux/arch/x86/kernel/apic/io_apic.c
> > ===================================================================
> > --- linux.orig/arch/x86/kernel/apic/io_apic.c   2010-09-17 13:00:19.164638447 -0500
> > +++ linux/arch/x86/kernel/apic/io_apic.c        2010-09-17 13:00:23.448595373 -0500
> > @@ -3253,6 +3253,11 @@ unsigned int create_irq_nr(unsigned int
> >                desc_new = move_irq_desc(desc_new, node);
> >                cfg_new = desc_new->chip_data;
> >
> > +#ifdef CONFIG_NUMA
> > +               if (node >= 0 && __assign_irq_vector(new, cfg_new, node_to_cpumask_map[node]) == 0)
> > +                       irq = new;
> > +               else
> > +#endif
> >                if (__assign_irq_vector(new, cfg_new, apic->target_cpus()) == 0)
> >                        irq = new;
> >                break;
> 
> target_cpus() for uv_x and x2apic phys mode all have cpu_online_mask()
> 
> so we should get the vector for other cpus. aka __assign_irq_vector()
> should not fail. unless you have so many irq > nr_irqs.

Did you even read the changelog ? It's not about "should".

All CPU0 vectors are assigned already just because the current code
takes the first cpu in the target_cpus mask regardless of the node on
which the irq_desc is allocated. That's crap. Why do we allocate
irq_desc on node and leave the vector assigned to node(cpu0) ?
 
> current code we only make sure irq_desc on device local node.

Brilliant.

> for the vectors, user can set irq smp_affinity move the device local
> cpus if needed.

What a nonsense. If we allocate irq_desc on a target node it does not
make any sense to target the vector to whatever random node/cpu in the
first place and wait for user space to fix it up. What about running
into that situation _before_ we hit user space ?

Thanks,

	tglx