What is SQL Server internal query execution thread scheduling (SOS Scheduler) and how does it manage CPU?

SOS Scheduler manages CPU execution for SQL Server workers using cooperative scheduling and run queues per scheduler.

SQL Server uses the SQLOS layer, where SOS Scheduler is responsible for distributing CPU time across worker threads. Each scheduler corresponds roughly to a CPU core and maintains runnable queues. SQL Server uses cooperative scheduling, meaning threads voluntarily yield CPU via SOS_YIELD rather than being preempted frequently. When a worker is running, it executes until it hits a yield point (like waiting on IO, lock, or quantum expiration). If workers overload a scheduler, you see SOS_SCHEDULER_YIELD waits.…