[Discuss-gnuradio] UHD host resources and system suggestions

[Marc Epard]

I'm a puzzled by some UHD behavior and wondering if I need a new host system. 
I'm not doing any signal processing in the host -- just transmitting from a 
buffer and/or receiving from a buffer. Later, we'll be wanting to do more 
processing with two USRP2s both transmitting and receiving at the same time and 
may want 25 Msps in some cases.

I've managed to get simultaneous receive threads going for each of two USRP2s, 
both at 25 Msps (big buffers are good). The GUI still updates, but is a little 
sluggish. It's fragile, though. If I do much at all with the GUI (sometimes 
just moving the mouse), recv's start timing out. System Monitor shows no memory 
pressure and both CPUs at 50-60%. FWIW, I'm running my C++ app via SSH from 
another machine.

Transmitting is worse. Even a solo transmit thread at 25 Msps (plus a thread 
calling recv_async_msg) causes the GUI to be unusable and I get frequent Us on 
both the host and the USRP2's serial port, as well as tons of 
EVENT_CODE_SEQ_ERROR and EVENT_CODE_SEQ_ERROR_IN_BURST messages from 
recv_async_msg. I can't tell what the CPU utilization is because System Monitor 
stops updating. 6.25 Msps is better, but I still get a few Us and a bunch of 
EVENT_CODE_SEQ_ERROR and EVENT_CODE_SEQ_ERROR_IN_BURST messages. System Monitor 
manages to update and shows CPU utilization of 80% and 55%. Again, I'm only 
transmitting from a buffer that I fill once up front and send over and over 
again  with no signal processing.
 
I'm specifying recv_buff_size=100e6 and send_buff_size=100e6; net.core.rmem_max 
and net.core.wmem_max are set to 100000000. I'm calling 
uhd::set_thread_priority_safe from each of my threads. I'm using the latest 
gnuradio and UHD software/firmware/FPGA (the recent release with USRP1 
support). I have Ubuntu 10.4 with stock ethernet drivers. 

I've itemized a few details of the hardware setup below. What systems are you 
all using for MIMO-like work with USRP2s and UHD? What systems do you recommend 
or wish you had? Are there other changes I should make to my current system?

TIA

-Marc

Dell DCDO tower manufactured in 2007
Dual-core Xeon 5110 @ 1.60 GHz
2 GB RAM
Lots of slots - mix of PCI, PCIe, PCI-X

Ethernet 0:  USRP2 with DBSRX
Onboard 10/100/1000 Ethernet. 
USRP2 says no flow control and we're getting another PCI Express card.

Ethernet 1: network connection
D-Link PCI NIC
No flow control

Ethernet 2:  USRP2 with XCVR2450
StarTech.com PCI Express 10/100/1000 Ethernet NIC 
Ubuntu identifies it as Broadcom NetXtreme BCM5752
USRP2 says it gets WE_TX flow control