[c-nsp] high CPU with ERSPAN on sup720

[Mark Boolootian]

Folks,

I'm trying to turn up an ERSPAN session on a sup720 w/PFC3BXL, and I'm
finding that my CPU is going from essentially idle to fully utilized
when being fed by two ports.

CPU utilization normally looks something like this:

 CPU utilization for five seconds: 2%/0%; one minute: 2%; five minutes: 3%

When I add the following config lines:

  monitor session 10 type erspan-source
   description ERSPAN_source_ISP_Sunnyvale
   source interface Gi2/11 - 12
   destination
    erspan-id 100
    ip address 192.168.11.11
    origin ip address 192.168.10.120

the CPU suddenly looks like this:

 CPU utilization for five seconds: 86%/72%; one minute: 21%; five minutes: 23%

The sup720 is supposed to take care of GRE in hardware, so I gather that isn't
the issue.  I've got a static route that points 192.168.11.11 to the interface 
address of a directly attached neighbor.  This box is running 12.2(18)SXE1.

Any ideas where I'm taking the hit?

Thanks,
mb