linux-kernel - Re: [RFC/PATCHv2] x86/irq: round-robin distribution of irqs to cpus w/in node

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Date:	Tue, 28 Sep 2010 00:12:55 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arthur Kepner <akepner@....com>
cc:	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC/PATCHv2] x86/irq: round-robin distribution of irqs to cpus
 w/in node

On Mon, 27 Sep 2010, Arthur Kepner wrote:

> On Mon, Sep 27, 2010 at 10:46:02PM +0200, Thomas Gleixner wrote:
> > ...
> > Sigh. Why is this a x86 specific problem ?
> >
> 
> It's obviously not. But we're particularly seeing it on x86 
> systems, so an x86-specific fix would address our problem.

Even more sigh.
  
> > If we setup an irq on a node then we should set the affinity to the
> > target node in general. 
> 
> OK.
> 
> > .... The round robin inside the node is really not
> > a problem unless you hit:
> > 
> >    nr_irqs_per_node * nr_cpus_per_node > max_vectors_per_cpu
> > 
> 
> No, I don't think that's true. 
> 
> The problem we're seeing is that one driver asks for a large 
> number of interrupts (on no CPU in particular). And because of the 

It does it for a node, dammit. Otherwise your patch would be
absolutely useless.

> > > +               if ((node != -1) && alloc_cpumask_var(&tmp_mask, GFP_ATOMIC)) {

> way that the vectors are initially assigned to CPUs (in 
> __assign_irq_vector()), a particular CPU can have all its vectors 
> consumed. 

Stop selling me crap already.

Thanks,

	tglx
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