linux-kernel - Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)

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Message-ID: <Pine.SGI.3.96.1080326163708.7873204c-100000@fergus.americas.sgi.com>
Date:	Wed, 26 Mar 2008 16:40:26 -0500 (CDT)
From:	Alan Mayer <ajm@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Alan Mayer <ajm@....com>, torvalds@...ux-foundation.org,
	linux-kernel list <linux-kernel@...r.kernel.org>,
	Robin Holt <holt@....com>, Jack Steiner <steiner@....com>,
	Russ Anderson <rja@....com>
Subject: Re: [PATCH] x86_64: resize NR_IRQS for large machines (re-submit)

On Wed, 26 Mar 2008, Ingo Molnar wrote:

> 
> * Alan Mayer <ajm@....com> wrote:
> 
> > On machines with very large numbers of cpus, tables that are 
> > dimensioned by NR_IRQS get very large, especially the irq_desc table.  
> > They are also very sparsely used.  When the cpu count is > 
> > MAX_IO_APICS, use MAX_IO_APICS to set NR_IRQS, otherwise use NR_CPUS.
> 
> thanks Alan, applied this in place of the other patch.
> 
> this bit is still ugly:
> 
> > -#define NR_IRQS (NR_VECTORS + (32 *NR_CPUS))
> > +#if NR_CPUS < MAX_IO_APICS
> > +#define NR_IRQS (NR_VECTORS + (32 * NR_CPUS))
> > +#else
> > +#define NR_IRQS (NR_VECTORS + (32 * MAX_IO_APICS))
> > +#endif
> >  #define NR_IRQ_VECTORS NR_IRQS
> 
> but it doesnt really depart from the current status quo of huge 
> [NR_IRQS] arrays either. Patches that make NR_IRQS a variable are 
> welcome :)
> 
> 	Ingo
> 

Good luck with that.  If i come up with something that's elegant enough
to make it worth the risk, I'll let you know.  Changing NR_IRQS to a variable
touches every arch and a lot of drivers.  Someone is bound to choke
on it, so it has to be something worth fighting for.

		--ajm

Lately it occurs to me,
What a long, strange trip it's been.
--
Alan J. Mayer
SGI
ajm@....com
WORK: 651-683-3131
HOME: 651-407-0134
--

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