netdev - Re: Network card IRQ balancing with Intel 5000 series chipsets

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Date:	Wed, 27 Dec 2006 09:09:34 +0200
From:	"Robert Iakobashvili" <coroberti@...il.com>
To:	hadi@...erus.ca
Cc:	"Arjan van de Ven" <arjan@...radead.org>, netdev@...r.kernel.org
Subject: Re: Network card IRQ balancing with Intel 5000 series chipsets

On 12/27/06, jamal <hadi@...erus.ca> wrote:
> On Wed, 2006-27-12 at 01:28 +0100, Arjan van de Ven wrote:
>
> > current irqbalance accounts for napi by using the number of packets as
> > indicator for load, not the number of interrupts. (for network
> > interrupts obviously)
> >
>
> Sounds a lot more promising.
> Although still insufficient in certain cases. All flows are not equal; as an
> example, an IPSEC flow with 1000 packets bound to one CPU  will likely
> utilize more cycles than 5000 packets that are being plain forwarded on
> another CPU.

I do agree with Jamal, that there is a problem here.

My scenario is treatment of RTP packets in kernel space with a single network
card (both Rx and Tx). The default of the Intel 5000 series chipset is
affinity of each
network card to a certain CPU. Currently, neither with irqbalance nor
with kernel
irq-balancing (MSI and io-apic attempted) I do not find a way to
balance that irq.

This is a good design in general to keep a static CPU-affinity for
network card interrupt.
However, what I have is that CPU0 is idle less than 10%, whereas 3
other core are
(2 dual-core CPUs, Intel) doing about nothing.
There is a real problem of CPU scaling with such design. Some day we
can wish to
add a 10Gbps network card and 16 cores/CPUs, but it will not be
helpful to scale.

Probably, some cards have separated Rx and Tx interrupts. Still,
scaling is an issue.

I will look into PCI-E option, thanks Jamal.

-- 
Sincerely,
Robert Iakobashvili,
coroberti %x40 gmail %x2e com
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