linux-kernel - Re: IRQ balancing on a router

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Message-ID: <20081003145737.GQ16624@fi.muni.cz>
Date:	Fri, 3 Oct 2008 16:57:37 +0200
From:	Jan Kasprzak <kas@...muni.cz>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: IRQ balancing on a router

Arjan van de Ven wrote:
: Jan Kasprzak <kas@...muni.cz> wrote:
: > The result is
: > that the CPU which receives IRQs for the uplink interface
: > is 100 % busy (softirq mostly), while the other one is 90% idle.
: 
: one of the hard cases for irqbalance is that irqbalance doesn't have a
: way to find out the actual cpu time spend in the handlers. For
: networking it makes an estimate just based on the number of packets
: (which is better than nothing)... but that breaks down if you have an
: non-symmetry in CPU costs per packet like you have.
: 
: The good news is that irqthreads at least have the potential to solve
: this "lack of information"; if not, we could consider doing a form of
: microaccounting for irq handlers....

	I am not sure whether this would help. In my case, the most of the
in-kernel CPU time is not spend in the irq handler per se, but in softirq
(i.e. checking the packet against iptables rules).

-Yenya

-- 
| Jan "Yenya" Kasprzak  <kas at {fi.muni.cz - work | yenya.net - private}> |
| GPG: ID 1024/D3498839      Fingerprint 0D99A7FB206605D7 8B35FCDE05B18A5E |
| http://www.fi.muni.cz/~kas/    Journal: http://www.fi.muni.cz/~kas/blog/ |
>>  If you find yourself arguing with Alan Cox, you’re _probably_ wrong.  <<
>>     --James Morris in "How and Why You Should Become a Kernel Hacker"  <<
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