[USRP-users] In search of 200 MSA/sec (Windows 7)

tilla at comcast.net tilla at comcast.net
Wed Mar 9 11:00:48 EST 2016


Over the past 2 weeks, I have been working towards achieving 200 MSA/sec on win7 64 bit, UHD 3.9.2, X310 w/WBX 120 daughtercard. 
  
I have a pretty good processor, 3.5 GHz Xeon E5-2637 v2, plenty of memory, 710-DA2 NIC in a x8 Gen 3 slot with verified Gen3 trained speed, a pretty beefy box in general. 
  
I have gathered a bunch of data and was looking for some further thoughts. 
  
I have done all the basic NIC tuning that is frequently discussed here: jumbo packets, disable interrupt coalescing, increase buffer sizes... 
  
I have done a huge amount of other tuning: disable numa, pcie performance mode, process affinitized to same cpu NIC is directly connected to, hyperthreading disabled, hand optimized compilation, and a boatload of other stuff. 
  
This is a simple prototype of a transmit only application, 1 thread, 1 transmit buffer, just send the same buffer as fast as possible.  Transmit loop is as simple as possible (bottom of page 2 in attachment). 
  
Attached is some performance data. 
  
50 MSA/sec, very good performance, occasional underflow, max cpu on a core ~35% (Figure 1 screenshots). 
  
100 MSA/sec, decent performance, more underflows but still "reasonable", max CPU on a core ~70% (Figure 2 screenshots). 
  
Handwave observable based upon above numbers: performance is linear, when sampling rate doubles, max CPU utilization doubles, perfectly expectable... 
  
Soooooo, now when going to 200 MSA/sec, constant underflows, not much transmission at all. 
  
Extrapolating based upon 100 MSA/sec numbers I would need ~140% of a CPU :(  (queue Charlie Brown music) 
  
If it is the byteswapping that is the true bottleneck, I am not sure there is really anything I can do as it is already SSE.  Unless do something like AVX or AVX2... 
  
On the recent thread titled "Throughput of PCIe Interface" we had some performance discussions.  I don't have the email available right now, but someone claimed 200 MSA/sec working.  I guess I am curious as to the setup. 
  
I would not think that byteswapping performance would vary much across operating systems... 
  
So I guess I am looking for any suggestions or thought anyone would have related to getting to 200 MSA, short of changing operating systems (for now). 
  
I am planning to evaluate Windows Server 2012 Standard in the near future if I cannot get this in some form of working, but would like to exhaust all options before investing that much time. 
  
Sorry for the long winded email. 
  
Thanks, 
  
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