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Re: [Discuss-gnuradio] UHD host resources and system suggestions

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] UHD host resources and system suggestions
Date: Fri, 03 Sep 2010 18:57:32 -0400
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On 09/03/2010 04:52 PM, Marc Epard wrote:
> Sorry to reply to myself, but we just got the new Ethernet NIC so both USRP2s 
> report WE_TX flow control. Nothing changed.
> And I have a correction for the types of ethernet cards. The onboard NIC is 
> the Broadcom. Ethernet 2 (and now 3) appear to be Realtek RTL8111/8168B.
> On Sep 3, 2010, at 3:10 PM, Marc Epard wrote:
I'll comment that a 1.6GHz machine that's getting close to 4 years old
isn't particularly "beefy" by todays standards.  Certainly not
  beefy enough to sustain two 25Msps threads without "problems".

Just the interrupt load alone is rather frightening.  The packets used
by the USRP2 aren't terribly big, something like 300-500 bytes
  I think.  So, 25e6 / 3e2 = 83Kpackets/second--depending on your NIC,
each of those packets could be creating an interrupt!

Then you have to actually process the darn things -- copy up to user
space, "do stuff", and present the result of that "stuff" either back out
  to the network, or into your software (FFT display, whatever).

To give some perspective.  I run my radio astronomy Rx-only "stack" on a
6-core machine doing "stuff" that's  of the same order of
  complexity as modern telecom-type signal processing.  At 5 or 6MHz
bandwidth, the machine is working *really* hard.  That's a machine
  with an AMD Phenom II X6 1090t, running at 3.2GHz/core with 6GB of
*fast* memory.  [And I suspect a flaky power supply, but that's
  a topic for another day :-) ].

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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