linux-kernel - Re: [RFC] irqbalance: Mark in-kernel irqbalance as obsolete, set to N by default

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Date:	Fri, 04 Aug 2006 07:36:06 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Andrew Morton <akpm@...l.org>
CC:	Auke Kok <auke-jan.h.kok@...el.com>, linux-kernel@...r.kernel.org,
	jesse.brandeburg@...el.com, john.ronciak@...el.com,
	netdev@...r.kernel.org
Subject: Re: [RFC] irqbalance: Mark in-kernel irqbalance as obsolete, set
 to N by default

Andrew Morton wrote:
> On Mon, 31 Jul 2006 10:35:26 -0700
> Auke Kok <auke-jan.h.kok@...el.com> wrote:
> 
>> We've recently seen a number of user bug reports against e1000 that the 
>> in-kernel irqbalance code is detrimental to network latency. The algorithm 
>> keeps swapping irq's for NICs from cpu to cpu causing extremely high network 
>> latency (>1000ms).
> 
> What kernel versions?  Some IRQ balancer fixes went in shortly after 2.6.17.
> 
> It would be better if poss to fix the balancer rather than deprecating it.

to some degree the in kernel balancer cannot really make the level of decisions that a
userspace balancer can make, at least not without making all kernel developers vomit ;)
(for example the userspace balancer looks in /proc/interrupts and parses that to see
which interrupts are used by networking versus which by storage etc, and has different
balancing policies for those and other classes; the networking policy basically comes down to
"pin the interrupt unless some higher networking interrupt really gets in the way")
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