Stephen Planck talks spinlocks:
High concurrency can expose subtle performance bottlenecks in SQL Server, particularly those stemming from spinlocks and latch contention. Both mechanisms exist to synchronize access to shared data structures, yet they operate differently and require distinct troubleshooting approaches. By recognizing how they work and knowing what causes them to overload a system, DBAs can reduce CPU spikes, timeouts, and overall application slowdowns.
Read on to more about spinlocks and latch contention. My experiential bias is that spinlocks are the actual problem approximately 5% of the number of times that DBAs believe spinlocks are the actual problem.