We are chasing high system utilization rates at our central location. When the CPU rate is low (between 5-15%) there is no TID named USL Task. When CPU runs high (between 94-98%) there is a TID named USL Tack running between 50-80%.
We have found many errors, loops, rogue APs, even a hub! After finding each of these our rmon stats broadcast/multicast numbers dropped and out CPU numbers came down to 5-15%. USL Task would go away. Check an hour later and the USL Task is back, churning up 50-75%, and CPU is hovering in the mid 90s. When it peggs at 100% things get really ugly since this is the main egress from the entire school district.
Spantree is enabled. Adminedge "should" be set on all non-edge ports. show spantree debug no longer shows any spantree issues. No adminedge ports are blocked. Only one loop has triggered spantree to this point.
We found a hub because of the number of collisions in rmon stats for that port (spantree wont pick up a hub - no bpdu's). This helped. A few days later CPU was pegged again and we found a loop in another switch in the subnet. Two of us have been combing through the 6 closets (with about 2-3 switches each) at this location for the past few days.
If USL Task is an indicator of a loop, we will keep looking for loops.