RE: CONFIG_IRQBALANCE for AMD64?

Nakajima, Jun
2004-05-28T17:10:34Z

>From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
>owner@vger.kernel.org] On Behalf Of Chris Wedgwood
>Sent: Thursday, May 27, 2004 2:38 PM
>To: Arjan van de Ven; Anton Blanchard
>Cc: Thomas Zehetbauer; 'linux-kernel@vger.kernel.org'
>Subject: Re: CONFIG_IRQBALANCE for AMD64?
>
>On Thu, May 27, 2004 at 06:50:25PM +0200, Arjan van de Ven wrote:
>
>> irqbalanced has NOT been obsoleted by CONFIG_IRQBALANCE.
>
>On Fri, May 28, 2004 at 03:03:34AM +1000, Anton Blanchard wrote:
>
>> > Seems to work, just like the i386 irqbalanced before it has been
>> > obsoleted by CONFIG_IRQBALANCE
>>
>> No, CONFIG_IRQBALANCE is an x86 specific hack.
>
The issue is a xAPIC thing, and the both kernel-level and user-level are
applicable to x86_64 as well.

The kernel does the default IRQ balancing, without assuming a user-level
irq balancing (because it's a distribution issue). If the user-level has
better knowledge, it just does a write to /proc/irq/N/smp_affinity to
bind that IRQ to a particular CPU, as Arjan's program is doing. In other
words, the kernel-level does _not_ move the ones bound by the
user-level.

>
>
>Why do we have CONFIG_IRQBALANCE at all then?
>
Today Linux is used for various configurations, including the ones that
substantially limit the set of user commands, libraries, etc. So we want
to keep it.

Jun

>
>
> --cw
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