[Discuss-gnuradio] uhd_rx_cfile: getting constant O-overflows using the USRP B200 with debian

[Ingmar Splitt]

Hi developers,

I have a fresh gnu radio installed with pybombs for my usrp B200. It runs on a 
Lenovo X230 with debian testing x64. 
When I use  uhd_rx_cfile i get constant "O"-overruns (output given below). 

The uhd-benchmark runs without problems:
    sudo ./benchmark_rate --duration 600 --rx_rate 32000000
So the USB3-Port isn't the Problem. Storing in ram is also fine:
    sudo ./uhd_rx_cfile -f 2445000000 --samp-rate=30000000 /tmp/test.cfile
I use a Samsung Evo 840 1TB (newest firmware) and did the SSD-Optimizations 
(https://wiki.debian.org/SSDOptimization) while searching for the error. 
HDPerm-, DD- and copy-benchmarks give 500mb/s for the first seconds, later 
constant ~400mb/s writing speed. 
Debugging with "iotop" brings (output below) 90% io-call-workload for the 
benchmarks, but 0% for the uhd_rx_cfile which writes only with 240mb/s. So 
everything should work as expected. 
Btw: I also get overruns (at a lower rate) when sampling with lower sample rate 
and try to change the nice number.

Have you got any idea how to find and fix the bottleneck?

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address@hidden:~/tools/grc/target/bin$ sudo ./uhd_rx_cfile -f 2445000000 
--samp-rate=30000000 /test/test.cfile -v

linux; GNU C++ version 4.8.2; Boost_105400; UHD_003.007.000-1-ga8caec5f

-- Operating over USB 3.
-- Initialize CODEC control...
-- Initialize Radio control...
-- Performing register loopback test... pass
-- Performing CODEC loopback test... pass
-- Asking for clock rate 32 MHz
-- Actually got clock rate 32 MHz
-- Performing timer loopback test... pass

UHD Warning:
    The hardware does not support the requested RX sample rate:
    Target sample rate: 30.000000 MSps
    Actual sample rate: 32.000000 MSps
Using mid-point gain of 36.5 ( 0.0 - 73.0 )
Motherboard: B200 (E6R04Z7B2)
Daughterboard: B200 (RX2, A:A)
Rx gain: 36.5
Rx baseband frequency: 2.445G
Rx DDC frequency: -596.046m
Rx Sample Rate: 32M
Receiving samples until Ctrl-C
Writing 32-bit complex floats
Output filename: /test/test.cfile
OOOOOOOOOOOO


#########################################

iotop

  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND          
                                   
  171 be/4 root        3.91 K/s    0.00 B/s  0.00 %  6.63 % [kworker/u16:3]
 2656 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.04 % X :0 -auth 
/var/run/lightdm~olisten tcp vt7 -novtswitch
 3502 be/4 root        0.00 B/s  236.78 M/s  0.00 %  0.00 % python2 
./uhd_rx_cfile -f 2~0000000 /test/test.cfile -v


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address@hidden:~/tools/grc/target/bin$ sudo hdparm -tT /dev/sda

/dev/sda:
 Timing cached reads:   17832 MB in  2.00 seconds = 8921.71 MB/sec
 Timing buffered disk reads: 1526 MB in  3.00 seconds = 508.55 MB/sec