CPU high because locking contention
When multiple threads fight over shared resources, the system burns CPU on coordination instead of useful work.
Common symptoms
- CPU high but throughput disappointing
- More concurrency makes things worse
- Latency spikes are unpredictable
Likely causes
- Mutex or lock contention
- Shared data structures under heavy load
- Critical sections that are too broad
Evidence to look for
perf shows spin or wait functions
Context switches correlate with latency
Reducing threads improves throughput
What it usually means
The machine is busy fighting over locks instead of doing productive work.
What to do next
- 1Narrow critical sections
- 2Reduce shared-state access
- 3Consider lock-free data structures for hot paths
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