[USRP-users] Problems with "uhd::set_thread_priority_safe"

Marcus D. Leech patchvonbraun at gmail.com
Thu Jul 2 19:41:33 EDT 2020


On 07/02/2020 01:11 AM, Nando Pellegrini wrote:
> Marcus ,
> The base Ubuntu version has only been 18.04 but i received updates 
> during ,let's say the past 7-10 days, the lap top is brand new and 
> 18.04 is the only Ubuntu version installed.
> I do n'ìt believe taht the USB has something to do with the problem , 
> USB is actually faster than the software taking samples from the 
> circular buffer used by the Etttus.
Not all USB3 controllers are created equal.  MANY of them are unable to 
support *sustained* transfer rates commensurate with the notional
   wire-speed. Ettus and Nuand discovered this many years ago when they 
introduced USB3-based products.  Some controllers simply cannot
   sustain long-term high-speed transfers, *despite* the CPU/PCIe/Memory 
adequacy of the system, which is why when there are performance
   issues on B2xx like this, I am often suspicious of the USB3 
controller.  This still happens today, and more often on lap-tops than 
desktop
   systems.

> My interpretation of "overflow error" is that the buffer is full and 
> samples are lost.
It means that the system isn't removing samples from the buffer as fast 
as they are arriving, on average, leading to dropped samples. This
   can be caused by inadequate attention to optimization in the software 
side, or it can (as I said above) be due to a poor-performing
   USB3 controller, inadequate long-term CPU/Memory/PCIe capacity, etc.


> Initialy i thought that the first event was the overflow error and 
> hence the priority was the designed guilt, now i have seen  that the 
> first event to happen is the drop of cpu speed and at 900Mhz is more 
> than reasonable to expect an overflow at more than 4 Gbits/second on 
> the USB.
> In addition, and as tried to explain to you, i saw the same running 
> pure CPU calculation during a prepfold operation with presto with a 
> frequency staying at 900 Mhz with 16 threads engaged in pure calculation.
> I could not find any information of which cpu is supported by Ubuntu 
> today and with which version, i saw that there is some concern between 
> the users about the combination Ubuntu + 10th generation intel cpu.
> nando
Certainly, inappropriate CPU throttling is very far outside the purview 
of the UHD drivers.



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