linux-kernel - Re: [PATCH] irq: crossbar: improve allocate_free

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Date:	Thu, 10 Apr 2014 16:55:27 -0500
From:	Felipe Balbi <balbi@...com>
To:	Felipe Balbi <balbi@...com>
CC:	<r.sricharan@...com>, <tglx@...utronix.de>, <galak@...eaurora.org>,
	<santosh.shilimkar@...com>, Darren Etheridge <detheridge@...com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irq: crossbar: improve allocate_free_irq() complexity

On Tue, Apr 01, 2014 at 05:44:19PM -0500, Felipe Balbi wrote:
> current algorithm in allocate_free_irq() is O(n),
> by just keeping track of last allocated IRQ with a
> simple unsigned integer, we can find a free IRQ
> in O(1).
> 
> Signed-off-by: Felipe Balbi <balbi@...com>
> ---
> 
> compile-tested only as J6 DTS is currently missing crossbar
> altogether :-(
> 
> There's a drawback with this patch which I'm not sure if we
> should care a lot because I couldn't entirely grasp when is
> domain->xlate() called and if we will map/unmap IRQs in runtime
> or will this *always* be done only during boot.
> 
> If we're talking about runtime IRQ remapping, then this, clearly,
> won't work. But if this will be done only during boot up, then we
> avoid iterating over the irq_map array each time we try to translate
> a new IRQ prior to mapping it.
> 
> Comments are highly welcome as I'll probably learn something new
> about the IRQ subsystem ;-)

do not apply this one!!! It won't work in all cases.

-- 
balbi

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