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

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Date:	Wed, 29 Sep 2010 20:05:40 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arthur Kepner <akepner@....com>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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 Wed, 29 Sep 2010, Arthur Kepner wrote:
> On Mon, Sep 27, 2010 at 05:17:07PM -0700, Eric W. Biederman wrote:
> > Thomas Gleixner <tglx@...utronix.de> writes:
> 
> On Tue, Sep 28, 2010 at 03:59:33AM -0700, Eric W. Biederman wrote:
> > Thomas Gleixner <tglx@...utronix.de> writes:
> > 
> > > On Mon, 27 Sep 2010, Eric W. Biederman wrote:
> > >> > On Mon, 27 Sep 2010, Arthur Kepner wrote:
> > >> The deep bug is that create_irq_nr allocates a vector (which it does
> > >> because at the time there was no better way to mark an irq in use on
> > >> x86).  In the case of msi-x we really don't know the node that irq is
> > >> going to be used on until we get a request irq.  We simply know which
> > >> node the device is on.
> > >
> > > Bah. So the whole per node allocation business is completely useless
> > > at this point.
> > 
> > Probably.
> 
> Huh? No, the patch that started this thread spreads the irqs around 
> and avoids the problem of a single CPU's vectors all being consumed.

I'm talking about the per node memory allocations for sparse. Not the
irq vectors
 
> > 
> > Understood.  It has taken a couple of years before this bug finally
> > bit anyone waiting a release or two to get it fixed properly seems
> > reasonable.
> > ....
> 
> And so what are we to do in the meantime? At the moment we're 
> disabling MSIX, which is a pretty unattractive workaround.

I understand that. The cleanup patches are hopefully ready for the
next kernel, so we can deal with that problem on top of them.

Thanks,

	tglx
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