linux-kernel - Re: [patch 20/47] x86: Remove useless reinitialization of irq descriptors

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Message-ID: <alpine.LFD.2.00.1010032014180.14550@localhost6.localdomain6>
Date:	Sun, 3 Oct 2010 20:26:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	David Woodhouse <dwmw2@...radead.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [patch 20/47] x86: Remove useless reinitialization of irq
 descriptors

On Sun, 3 Oct 2010, Eric W. Biederman wrote:

> Thomas Gleixner <tglx@...utronix.de> writes:
> 
> > The descriptors are already initialized in exaclty this way.
> 
> They aren't only status is initialized exactly that way.

Err.

SPARSE_IRQ=n:

struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
        [0 ... NR_IRQS-1] = {
                .status = IRQ_DISABLED,
		.chip = &no_irq_chip,
                .handle_irq = handle_bad_irq,
                .depth = 1,
                .lock = __RAW_SPIN_LOCK_UNLOCKED(irq_desc->lock),
        }
};

So action == NULL and depth == 1

SPARSE_IRQ=y:

allocates with kzalloc which makes action == NULL and depth is set in
the init function to 1.

That's true for mainline and after the rework as well.

Thanks,

	tglx
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