The CPU profile reveals significant contention around condition variables and system calls, indicating a high likelihood of thread synchronization bottlenecks and potentially inefficient I/O operations.
1. Main Performance Bottlenecks:
Condition Variable Waits (pthread_cond_timedwait, std::condition_variable::wait_until): These functions account for a massive portion (nearly 60%) of the cumulative execution time. This strongly suggests threads are spending excessive time waiting on each other for resources or synchronization points. The high percentage in both self and cumulative time points to a problem within the wait_until implementation itself, rather than just the frequency of calls.
System Calls (do_syscall_64): A substantial portion of time is spent in system calls, hinting at potential inefficiencies in I/O operations or excessive context switching. The high percentage suggests a large number of relatively small system calls, rather than a few large ones.
Task Switching (finish_task_switch): A significant percentage of time is spent on task switching, further supporting the hypothesis of excessive context switching due to contention.
2. Functions/Areas Needing Optimization:
resdb::ReplicaCommunicator::StartBroadcastInBackGround::{lambda#1}::operator const: This lambda function within the ReplicaCommunicator class is a major contributor to the cumulative time. Investigate its logic for potential blocking operations or inefficient algorithms.
resdb::MessageManager::GetResponseMsg: While a smaller contributor, this function's involvement in the cumulative time warrants investigation for potential synchronization issues or blocking calls.
Condition Variable Usage: The entire mechanism using condition variables needs a thorough review. Consider:
System Call Optimization: Profile the code to identify the specific system calls within do_syscall_64. Are there opportunities to reduce the number of calls, batch them, or use more efficient I/O methods (e.g., asynchronous I/O)?
3. Specific Recommendations:
Profiling with higher resolution: Use a profiler that provides more detailed information about the call stack within the identified bottlenecks (e.g., perf with appropriate sampling options). This will pinpoint the exact lines of code causing the delays.
Code Review of ReplicaCommunicator and MessageManager: Carefully review the code within these classes, focusing on the identified functions and their interactions with condition variables and other synchronization primitives.
Implement asynchronous operations: If I/O is a bottleneck, consider using asynchronous I/O operations to avoid blocking threads while waiting for data.
Optimize condition variable usage: Refactor the code to minimize the time spent waiting on condition variables. Consider using techniques like condition variable notification optimization or replacing condition variables with more efficient alternatives where appropriate.
Thread Pooling: If many short-lived tasks are creating and destroying threads, consider using a thread pool to reduce the overhead of thread creation and destruction.
Memory Allocation Profiling: While not directly indicated here, memory allocation can indirectly impact performance. Consider profiling memory usage to rule out excessive allocations or deallocations contributing to the observed slowdowns.
By addressing these bottlenecks and implementing the suggested optimizations, significant performance improvements should be achievable. The focus should be on reducing contention around condition variables and optimizing system call usage. Remember to measure performance after each optimization step to verify its effectiveness.