linux-kernel - Re: [PATCH 4/5] x86: Add config variables for SMP

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Message-Id: <20080128104520.e1e6c878.pj@sgi.com>
Date:	Mon, 28 Jan 2008 10:45:20 -0600
From:	Paul Jackson <pj@....com>
To:	Mike Travis <travis@....com>
Cc:	ioe-lkml@...eria.de, akpm@...ux-foundation.org, ak@...e.de,
	mingo@...e.hu, clameter@....com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] x86: Add config variables for SMP_MAX

Ten days ago, Mike wrote:
> The primary problem arises because of cpumask_t local variables.  Until I
> can deal with these, increasing NR_CPUS to a really large value increases
> stack size dramatically.
> 
> Here are the top stack consumers with NR_CPUS = 4k.
> 
>                          16392 isolated_cpu_setup
>                          10328 build_sched_domains

The problem in kernel/sched.c:isolated_cpu_setup() is an array of
NR_CPUS integers:

    static int __init isolated_cpu_setup(char *str)
    {
	    int ints[NR_CPUS], i;

	    str = get_options(str, ARRAY_SIZE(ints), ints);

Since isolated_cpu_setup() is an __init routine, perhaps we could
make that ints[] array static __initdata?

The build_sched_domains() may require more thought and code rework.
See also the lkml discussion of my patches that reworked the cpuset
code implementing 'sched_load_balance' calling into build_sched_domains
() via kernel/sched.c:partition_sched_domains().  This is not performance
critical code, fortunately.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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