Subject: Re: ppc_irq_dispatch_handler dominating profile?

From: Fred Gray <[email-masked]>
Date: Mon, 28 Apr 2003 05:42:24 -0700

On Mon, Apr 28, 2003 at 10:53:42AM +0200, Gabriel Paubert wrote:
> Hmmm, I get more than 100MB/s on my MVME2600 with a 200MHz 603e,
> although not the half GB/s Motorola claims it is capable of. But a 604
> should be a bit faster. The chipset is old (1997) but it was rather
> fast when it came out, especially because the memory interface is 128
> bits wide. This said, putting a gbit Ethernet (PMC module I suppose)
> on it is stretching it a bit.
>
> Is the 100Mb/s of the builtin interface too slow for you?

Hi, Gabriel, (...and many thanks for your hard work porting Linux to these
  boards in the first place--I am extremely glad to be in a position to leave
  vxWorks behind)

The gigabit Ethernet is indeed on a PMC module (from SBS Technologies,
PMC-Gigabit-ST3).  Our electronics generates about 15 MB/s per VME crate;
it's digitizing tracks left by muons in a time-projection chamber.
There are two crates, each with this rate, each equipped with an MVME2600
with an gigabit card, and they have to transfer this firehose of data to a
computer that will do some as-yet-undefined online data reduction and
send the result to an LTO 2 tape robot.  So, yes, we need about 50% more
throughput than the built-in 10/100 Ethernet port could provide, and we need
it with enough CPU time left over to manage the VME readout.

Fortunately, though, we don't need the whole gigabit.  I agree that would
probably be well-nigh impossible.  Still, I'm very interested in understanding
why the interrupt overhead seems to be so high at our 10 to 15 MB/s
interrupt rate.

Thanks,

-- Fred

-- Fred Gray / Visiting Postdoctoral Researcher                         --
-- Department of Physics / University of California, Berkeley           --
-- [email-masked] / phone 510-642-4057 / fax 510-642-9811 --

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