Switch policy design

Current swilock components & implementation status

• Lock & Unlock APIs✅

  • Switch between CAS, qspinlock, TCLock (queue-based)

• Helper thread✅

  • Change lock type every 5s

• FFWD⭕️

  • Server thread: iterate through CPU requests, switch stack and process requests
  • Client APIs: delegate() & delegate_finish(), can replace lock() & unlock()

• Throughput live demo✅

Switch base on contention

Plan A

Consider how many threads are using the lock.

1. Add a global counter
2. When calling lock() & unlock(), increase & decrease counter
3. Helper thread checks the counter, switch lock base on its value, e.g.
   • (0,1] CAS
   • [2,8] qspinlock
   • (8,+inf) TCLock

Plan B

Consider how long the threads have been waiting

1. For each thread, calculate time between lock() & unlock()
2. Helper thread maintains recent waiting times (e.g. 32 lateast values)
3. Helper thread switch base on average waiting time?

Can also keep statistics of:

1. waiting time
2. overall throughput