[USRP-users] libusb uses only one thread?

Marcus D. Leech mleech at ripnet.com
Mon Oct 23 01:10:07 EDT 2017

On 10/22/2017 05:09 PM, Андрій Хома via USRP-users wrote:
> Hello,
> I have:
> 6 usrp b502mini
> The motherboard Z10PE-D16 WS (can it matter in the chipset?)
> Intel xeon e5-2430v4 processor
> Memory DDR4 1866 (128 GB)
> As a result I get overflow ("O") when using 6 usrp at once.
> I'm not proficient in profiling, but I saw that only one thread is 
> created for libusb, maybe this is the bottleneck.
> Explanation of attached picture # 1:
> 1 Create / initialize devices
> 2 I create two threads for each device, they alternate in the picture:
>     one on "recv" (starting from the very first). It can be seen that 
> it is quite resource intensive, basically time is spent on 
> convert_sc12_item32, but it's clear that the CPU core copes less
>     the second to write to named fifo (those that are more 
> intermittent, starting with the second). Also is not resource-intensive.
> 3 I understand that in this thread there lives libusb, and it's only 
> one, for 6 devices (see picture number 2)
> Also, I was playing with usrp x310, and I work quietly with 400Msps 
> (via dual 10G ethernet), ie convert_sc12_item32 is fully capable of 
> processing 400Msps on one 2.2GHz core, so the bottleneck is the 
> aforementioned single libusb stream.
> Did I make the right conclusions?
> If so, then I need to know exactly what CPU power I need, without 
> guessing on the coffee grounds.
> Are there any benchmarks, hardware requirements, so that I can still 
> use these devices?
This document on libusb may be of some elucidation.


Also, you didn't mention what your sample-rates are, and the USB-3.0 
hardware subsystem can matter a lot.

Also, you can look into using num_recv_frames in your device arguments 
to "tune" the use of the USB subsystem.


> Встроенное изображение 1
> Встроенное изображение 2
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