linux-kernel - Re: [RFC 07/13] sched: Reduce stack size requirements in kernel/sched.c

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Message-ID: <48C53D20.604@sgi.com>
Date:	Mon, 08 Sep 2008 07:56:32 -0700
From:	Mike Travis <travis@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, davej@...emonkey.org.uk,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jack Steiner <steiner@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jes Sorensen <jes@....com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 07/13] sched: Reduce stack size requirements in kernel/sched.c

Peter Zijlstra wrote:
> On Sun, 2008-09-07 at 04:00 -0700, Andrew Morton wrote:
>> On Sun, 07 Sep 2008 12:24:47 +0200 Peter Zijlstra <peterz@...radead.org> wrote:
>>
>>> get_online_cpus() can sleep, but you just disabled preemption with those
>>> get_cpumask_var() horribles!
>> make cpu_hotplug.refcount an atomic_t.
> 
> A much easier fix is just re-ordering those operations and do the
> get_online_cpus() before disabling preemption. But it does indicate this
> patch series isn't carefully constructed.

Yes, it's mostly a hunt for comments on my part... ;-)
> 
>>> Couldn't be arsed to look through the rest, but I really hate this
>>> cpumask_ptr() stuff that relies on disabling preemption.
>> that's harder to fix ;)
> 
> Looking at more patches than just the sched one convinced me more that
> this approach isn't a good one. It seems to make code much more
> fragile. 
> 
> See patch 9, there it was needed to draw out the callgraph in order to
> map stuff to these global variables - we're adding global dependencies
> to code that didn't have any, increasing complexity.

Again, yes, as I got farther into that one, it became clear that having
static cpumask_t temps over too large a range was ending up very messy.

Thanks,
Mike

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