linux-kernel - Re: [PATCH 07/14] genirq: Add a new generic IPI reservation code to irq core

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Date:	Mon, 16 Nov 2015 16:09:32 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Qais Yousef <qais.yousef@...tec.com>
cc:	linux-kernel@...r.kernel.org, jason@...edaemon.net,
	marc.zyngier@....com, jiang.liu@...ux.intel.com,
	ralf@...ux-mips.org, linux-mips@...ux-mips.org
Subject: Re: [PATCH 07/14] genirq: Add a new generic IPI reservation code to
 irq core

On Mon, 9 Nov 2015, Qais Yousef wrote:
> On 11/07/2015 01:31 PM, Thomas Gleixner wrote:
> > On Tue, 3 Nov 2015, Qais Yousef wrote:
> > > +
> > > +	/* always allocate a virq per cpu */
> > > +	nr_irqs = ipi_mask_weight(dest);
> > That's not really a good assumption. Not all architectures need
> > seperate interrupt numbers / descriptors because they can allocate
> > from a per cpu interrupt space. We really want to handle that here as
> > well. So we need a flag in the IPI domain which tells us whether that
> > allocation needs to be weight(desc) or 1.
> 
> OK. But is it bad to always allocate the weight? I thought allocating virqs is
> cheap, or maybe not?

It's wrong to allocate the descriptors in the case of per cpu
interrupts. Aside of wasting memory its not representing what the
hardware does.

Thanks,

	tglx
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