[c-nsp] association between TCAM usage and CPU load in L3 switch

[Martin T]

Hi,

I have a Cisco ME-3600X-24FS-M switch which supports up to 20000
unicast IPv4 prefixes with SDM profile in use. If I announce full BGP
table to this switch and exhaust all the TCAM available for unicast
IPv4 prefixes:


ME3600X#sh platform tcam utilization ucastv4
Nile Tcam Utilization per Application & Region:
ES == Entry size == Number of 80 bit TCAM words
==================================================================
App/Region            Start  Num Avail  ES    Used Range  Num Used
==================================================================
UCASTV4                   0     20480   1
    nile0                                                    20000
    nile1                                                    20000


..then CPU load will be around 100%:


      111 111
      00090009     1             1  1         1
      000900099999609899888998999099399999999909788888889888998899
  100 #######*
   90 #######*
   80 #######*
   70 #######*
   60 ########
   50 ########
   40 ########
   30 ########
   20 ########
   10 ########**************************************************
     0....5....1....1....2....2....3....3....4....4....5....5....6
               0    5    0    5    0    5    0    5    0    5    0
               CPU% per minute (last 60 minutes)
              * = maximum CPU%   # = average CPU%

According to "sh ip route summary", RAM usage for BGP was around
85MiB. What exactly is causing such high CPU usage? I should have run
"sh processes cpu sorted 5min" during the high CPU usage, but forgot
to do so.



regards,
Martin