linux-kernel - Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig

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Date:	Mon, 07 Aug 2006 11:46:25 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Randy.Dunlap" <rdunlap@...otime.net>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@...e.de>,
	"Protasevich, Natalie" <Natalie.Protasevich@...SYS.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig

"H. Peter Anvin" <hpa@...or.com> writes:

> Eric W. Biederman wrote:
>> a) Because I would like to flush out bugs.
>> b) Because I want a default that works for everyone.
>> c) Because with MSI we have a potential for large irq counts on most systems.
>> d) Because anyone who disagrees with me can send a patch and fix
>>    the default.
>> e) Because with the default number of cpus we can very close to needing
>>    this many irqs in the worst case.
>> f) This is much better than previous to my patch and setting NR_CPUS=255
>>    and getting 8K IRQS.
>> g) Because I probably should have been more inventive than copying the
>>    NR_IRQS text, but when I did the wording sounded ok to me.
>>
>
> Why not simply reserve 224*NR_CPUS IRQs? If you have 256 CPUs allocating 64K
> IRQs should hardly matter :)

Well there is this little matter of 224*NR_CPUS*NR_CPUS counters at that point
that I think would be prohibitive for most sane people.  Taking 224K of per cpu
memory in 256 different per cpu areas.

Still what is 56MB when you have a terrabyte of RAM. :)

Eric
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