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SubjectRe: Gigabit Linux Server Bottlenecks
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On 08-Feb-2000 John LeMay wrote:
> Craig,
>
> You have pointed out, very delicately, a major limitation of Ethernet as
> it is implemented today. I find myself constantly arguing against
> implementation of gig Ethernet due to the high CPU cost on the host
> system. Trying to fill a gig pipe with 1,514 byte packets is, IMHO,
> maddening to the CPU. As I recall, the host must be able to process
> around 82,000 packets (read "CPU interrupts") per second to fill the

Wrong. All GigE cards I have checked so far have interrupt mitigation. At init
you program them to delay IRQ until that many packets are in the queue or a
timer expires and the timer value. The only problem is that these are usually
not passed as module params. So you have to recompile if you find your current
mitigation params bad.

> pipe unidirectionally. Try this in a full duplex setting with a 2 gig
> pipe to fill and you (at least) double the amount of work the CPU needs
> to accomplish every second.

Wrong, see above.

>
> Since no one seems to want to jump on the 8K jumbo frames bandwagon

See above. If you program a sane GigE NIC correctly you actually transfer more
than 8K at a time. Donald Becker's hamachi driver is a good example.

> Alteon has embraced, current technology and CPU speeds seem to indicate
> more "bang for the buck" with a couple of trunked Fast Ethernet links.
> The last thing one wants to do, no matter what NOS you choose, is
> overrun the host CPU. Depending on the environment, it may even be less
> expensive when all things are considered to implement a Token Ring
> solution!

[snip][snip][snip]

- ----------------------------------
Anton R. Ivanov
IP Engineer Level3 Communications
RIPE: ARI2-RIPE E-Mail: Anton Ivanov <aivanov@eu.level3.net>
@*** Programmer's Evidence ***
Programming is a series of discoveries leading you
from one plateau of understanding to another...
The trick is not to step in the stuff between the plateaus.

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