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Network Gbit Performance on TWR-LS1021A - high CPU utilization

Question asked by Reinhard Tartler on Sep 8, 2015
Latest reply on Sep 11, 2015 by Yiping Wang

Using a TWR-LS1021A board with SDK v1.8 (Linux 3.12.370rt51)


I've configured eth0 following the recommendations from Test Procedure


root@ls1021atwr:~# ethtool -C eth0 rx-frames 22

root@ls1021atwr:~# ethtool -C eth0 tx-frames 22

root@ls1021atwr:~# ethtool -C eth0 rx-usecs 32

root@ls1021atwr:~# ethtool -C eth0 tx-usecs 32

root@ls1021atwr:~# ethtool -K eth0 gro on gso on sg on


root@ls1021atwr:~# netperf -H -l 10  -T 1 -c 100 -C 100 -n2 -t TCP_SENDFILE -v 2 -- -C

TCP SENDFILE TEST from () port 0 AF_INET to () port 0 AF_INET : cpu bind

Recv   Send    Send                          Utilization       Service Demand

Socket Socket  Message  Elapsed              Send     Recv     Send    Recv

Size   Size    Size     Time     Throughput  local    remote   local   remote

bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB


87380  16384  16384    10.03       886.20   76.23    18.60    14.094  3.439 


Alignment      Offset         Bytes    Bytes       Sends   Bytes    Recvs

Local  Remote  Local  Remote  Xfered   Per                 Per

Send   Recv    Send   Recv             Send (avg)          Recv (avg)

    8       8      0       0 1.111e+09  16384.00     67799   23129.53  48026




Size (bytes)



In this setup, the other side is a Core2Duo x86 laptop @2.9 Ghz.


Using strace, I can confirm that netperf is indeed using the sendfile64 syscall:


root@ls1021atwr:~# grep -c sendfile64 netperf.strace




The achieved bandwidth is less than we hoped, and the CPU utilization is unacceptably high. This is already after:


Why is the CPU utilization still so extremely high, and what can be done to improve this further?