linux-kernel - Re: [PATCH 5/5] x86: update nr

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Message-ID: <4B4785C3.4030505@zytor.com>
Date:	Fri, 08 Jan 2010 11:21:39 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] x86: update nr_irqs according cpu num

On 01/08/2010 11:11 AM, Eric W. Biederman wrote:
> Yinghai Lu <yinghai@...nel.org> writes:
> 
>> that is max number on run time.
> 
> Ouch!  Unless I misread this code this will leave nr_irqs at
> NR_IRQS_LEGACY. aka 16.
> 
> Let's do something stupid and simple.
> nr_irqs = nr_cpus_ids * 256;  /* Semi-arbitrary number */

This would be 1048576 on the biggest machines we currently support.
Now, the number of IRQ *vectors* is limited to
(224-system vectors)*(cpu count), so one could argue that if there is
anything that is not semi-arbitrary it would be that number, but that
doesn't account for vector sharing.

Do we have any place which requires nr_irqs to be *stable*, or can we
simply treat it as a high water mark for IRQ numbers used?

> Ideally we would set "nr_irqs = 0x7fffffff;" but we have just enough
> places using nr_irqs that I think those loops would get painful if we
> were to do that.

Ideally we should presumably get rid of nr_irqs completely?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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