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Date: Wed, 26 Mar 2008 18:55:54 +0200 From: Adrian Bunk <bunk@...nel.org> To: Mike Travis <travis@....com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/2] x86: Modify Kconfig to allow up to 4096 cpus On Wed, Mar 26, 2008 at 09:31:22AM -0700, Mike Travis wrote: > Adrian Bunk wrote: > > On Tue, Mar 25, 2008 at 06:41:39PM -0700, Mike Travis wrote: > >> Increase the limit of NR_CPUS to 4096 and introduce a boolean > >> called "MAXSMP" which when set (e.g. "allyesconfig"), will set > >> NR_CPUS = 4096 and NODES_SHIFT = 9 (512). > > > > > > I'm not really getting the point of MAXSMP - people should simply pick > > their values, and when they want the maximum "(2-4096)" and "(1-15)" > > already provide this information (except that your patch hides the > > latter information from the user). > > > > And with your patch, even with MAXSMP=y people could still set > > NR_CPUS=7 and NODES_SHIFT=15 or whatever else they want... > > > > More interesting would be why you want it to set NODES_SHIFT to > > something less than the maximum value of 15. I'm getting the fact that > > 2^15 > 4096 and that 15 might be nonsensical high, but this sounds more > > like requiring a patch to limit the range to 9? > > I guess the main effect is that "MAXSMP" represents what's really > usable for an architecture based on other factors. The limit of > NODES_SHIFT = 15 is that it's represented in some places as a signed > 16-bit value, so 15 is the hard limit without coding changes, not > an architecture limit. This is the x86-specific Kconfig file that presents the x86 specific limits to the users. If NODES_SHIFT=15 is offered to the user although it's higher than the current architecture limit on x86 then this is simply a bug that should be fixed. > Thanks, > Mike cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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