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Date: Thu, 06 Jun 2002 12:48:57 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Robert Love <rml@tech9.net>
CC: "David S. Miller" <davem@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] CONFIG_NR_CPUS
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Robert Love wrote:
> 
> On Thu, 2002-06-06 at 03:15, David S. Miller wrote:
> 
> > Nice.  While you're at it can you fix the value on 64-bit
> > platforms when CONFIG_NR_CPUS is not specified?  (it should
> > be 64, not 32)
> 
> I agree, this is good.  I often am toying with some debugging aid that
> is an array of NR_CPUS and waste a lot of memory with NR_CPUS stuck at
> 32... no reason my kernels should not be set to 2 or whatever I need.
> 
> I have attached a patch that is Andrew's + your request, Dave.  Since
> what really determines the maximum number of CPUs is the size of
> unsigned long, I used that.  Cool?
> 
> ...
> +#define NR_CPUS        (sizeof(unsigned long) * 8)

OK.  What I'll do is:

#ifdef CONFIG_SMP
#define NR_CPUS CONFIG_NR_CPUS
#else
#define NR_CPUS 1
#endif

and then go edit every SMP-capable arch's config.in/Config.help
files.  But the arch maintainers should test one case please - x86
was locking up at boot on quad CPU with NR_CPUS=2.  Others may do
the same.

About a quarter of the bloat is runqueues.  If we could dynamically
allocate those in sched_init() it would be good, because presumably
vendor kernels will be configured for the maximum number of CPUs.

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