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

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Date:	Tue, 19 Oct 2010 16:58:42 -0700
From:	Arthur Kepner <akepner@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [RFC/PATCHv2] x86/irq: round-robin distribution of irqs to
	cpus w/in node

On Sun, Oct 17, 2010 at 12:44:07PM +0200, Thomas Gleixner wrote:
> ....
> Looked a bit deeper into the users. Quite a bunch do
> 
>        pci_enable_msix();
>        request_irqs();
> 
> in their probe function. There is no sign of making them per cpu or
> node. mlx4 is one of them. No sign of anything related to nodes or cpus in
> the whole driver.
> 
> Even if the driver does not request the irqs from the probe function,
> why does it need to do the msi/msix setup in the probe function at
> all?
> 
> Wouldn't it be sufficient to do that at open() right before the
> interrupts are requested.

That's a good point.

> .....
> The fundamental flaw of arch_setup_msi_irqs() is 
> 
>   node = dev_to_node(&dev->dev);
> 
> That's the only node information we get. So we put everything on a
> single node.
>

But it's even worse than that, because we put everything on a single 
cpu within the node until no vectors are left there, then move on to the 
next one...

-- 
Arthur
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