linux-kernel - Re: CONFIG_IRQBALANCE for 64-bit x86 ?

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Message-ID: <p7363zwbuai.fsf@bingen.suse.de>
Date:	Tue, 20 Nov 2007 20:17:57 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Mark Lord <lkml@....ca>, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: CONFIG_IRQBALANCE for 64-bit x86 ?

Nick Piggin <nickpiggin@...oo.com.au> writes:
>
> For that matter, I'd like to know why it has been decided that the
> best place for IRQ balancing is in userspace.

There is a lot of possible policy in it 

> It should be in kernel
> IMO, and it would probably allow better power saving, performance,
> fairness, etc. if it were to be integrated with the task balancer as
> well.

Integrating with the task balancer makes really only sense if the
device supports MSI-X and if it does that you don't really need
an irq balancer because you can just send to all CPUs as needed.

Without MSI-X you would be trying to reprogram the interrupts
all the time when a task is migrating and it is highly doubtful
that doing that automatically would do any good.

-Andi

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