[c-nsp] high cpu usage because of process switching on mlppp interface

[Arda Balkanay]

Hi
i have a problem about high cpu usage on a 7206 VXR NPE-G1 because of
process switching on a multilink ppp interface.

I have two E1 interfaces between 7206 and 3845 (below MTP-C72-02 indicates
7206 and ADN-C38-01 indicates 3845).
I've bundled these two E1 interfaces. And when the amount of traffic rised
CPU usage also increased about 15 percent more.
"show proc cpu" output points increase at the processes of ip input and tag
input.
MTP-C72-02#sh proc cpu sorted
CPU utilization for five seconds: 78%/64%; one minute: 79%; five minutes:
81%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  68    39242000 258183793        151  8.92%  8.20%  8.40%   0 IP
Input
 109    25093708 119681214        209  6.88%  7.37%  7.79%   0 Tag Input


When i looked at the switching status of the interface i saw that 7206 is
using process switching while 3845 uses fast switchig (especially for mpls)
MTP-C72-02#sh inter mul 1 switching
Multilink1 Maltepe - Adana MLPPP
          Throttle count          0
                   Drops         RP     752707         SP          0
             SPD Flushes       Fast          0        SSE          0
             SPD Aggress       Fast          0
            SPD Priority     Inputs        259      Drops          0

    Protocol  IP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process   50148189  395174672     261949   26235771
            Cache misses          0          -          -          -
                    Fast       1325     105874      12194     724886
               Auton/SSE          0          0          0          0

    Protocol  Tag
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process   79390997 3601460527       5116     538398
            Cache misses          0          -          -          -
                    Fast          0          0   87354606 4071850482
               Auton/SSE          0          0          0          0


ADN-C38-01#sh inter mu 1 switching
Multilink1 Adana - Maltepe MLPPP
          Throttle count          0
                   Drops         RP          0         SP          0
             SPD Flushes       Fast          0        SSE          0
             SPD Aggress       Fast          0
            SPD Priority     Inputs        242      Drops          0

    Protocol  IP
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process      32394    2110804      17595    1260300
            Cache misses          0          -          -          -
                    Fast     559376   60411948        154       8439
               Auton/SSE          0          0          0          0

    Protocol  Tag
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
                 Process       7106     398899      10784     539203
            Cache misses          0          -          -          -
                    Fast   87130476 3140243335   80454345  488241675
               Auton/SSE          0          0          0          0


When i checked "show ip interface" output i can see that fast swithing is
enabled but i didn't understand why 7206 uses process switching while 3845
uses fast
swithcing with the same multilink interface configuration. ip interface
output is as follows:

MTP-C72-02#sh ip int mu 1
Multilink1 is up, line protocol is up
...
  IP fast switching is enabled
  IP fast switching on the same interface is enabled
  IP Flow switching is disabled
  IP CEF switching is enabled
  IP CEF Fast switching turbo vector
  IP Null turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast, CEF
  ...
MTP-C72-02#

ADN-C38-01#sh ip int mu 1
Multilink1 is up, line protocol is up
  ...
  IP fast switching is enabled
  IP fast switching on the same interface is enabled
  IP Flow switching is disabled
  IP CEF switching is enabled
  IP CEF Fast switching turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast, CEF
  ...
ADN-C38-01#
7206 uses ios c7200-jk9s-mz.123-14.T3.bin and 3845 uses
c3845-spservicesk9-mz.124-8b.bin


Do you have any idea about this situation ?


Kind Regards
Arda