linux-kernel - Re: [RFC 09/13] genapic: reduce stack pressuge in io_apic.c step 1 temp cpumask

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Message-ID: <8763p6vr3b.fsf@basil.nowhere.org>
Date:	Mon, 08 Sep 2008 13:01:44 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 09/13] genapic: reduce stack pressuge in io_apic.c step 1 temp cpumask_ts

Mike Travis <travis@....com> writes:

>   * Step 1 of cleaning up io_apic.c removes local cpumask_t variables
>     from the stack.

Sorry that patch seems incredibly messy. Global variables
and a tricky ordering and while it's at least commented it's still a mess
and maintenance unfriendly.

Also I think set_affinity is the only case where a truly arbitary cpu
mask can be passed in anyways. And it's passed in from elsewhere. 

The other cases generally just want to handle a subset of CPUs which
are nearby. How about you define a new cpumask like type that 
consists of a start/stop CPU and a mask for that range only 
and is not larger than a few words?

I think with that the nearby assignments could be handled 
reasonably cleanly with arguments and local variables.

And I suspect with some restructuring set_affinity could
be also made to support such a model.

-Andi
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