The backtrace you provided shows the call stack for a QEMU process running on Linux. It includes information about the threads involved and their execution paths. Here's a breakdown of what the trace indicates: ### Thread 1 (Main Thread) - **Function Call**: `__ppoll` This is a system call related to polling file descriptors, likely waiting for I/O operations to complete. - **Call Path**: - `qemu_poll_ns`: QEMU's custom polling function. - `os_host_main_loop_wait`: Part of the main loop that handles events and timeouts. - `main_loop_wait`: The main loop that runs the QEMU simulation. - `qemu_default_main`: The default main function for QEMU. - `__libc_start_call_main` and `_start`: Standard C library initialization. ### Thread 2 (Secondary Thread) - **Function Call**: `syscall` This indicates a system call, possibly related to threading or synchronization. - **Call Path**: - `qemu_futex_wait`: A QEMU-specific function for waiting on a futex (fast userspace mutex). - `qemu_event_wait`: Another QEMU-specific function for event handling. - `call_rcu_thread`: Handles call-scheduler events in the Real-Time Clock (RTC) library. - `qemu_thread_start`: Starts a new thread in QEMU. - `start_thread` and `clone3`: Standard C library functions for thread creation. ### Key Observations: 1. **QEMU Threads**: The process has multiple threads, including the main thread and at least one secondary thread. 2. **System Calls**: Both threads involve system calls (`__ppoll` and `syscall`), indicating they are waiting for I/O or other events. 3. **Event Handling**: The use of futexes and event waiting suggests QEMU is handling asynchronous events in a non-blocking manner. ### What This Might Mean: - If you're debugging performance issues, this trace shows that QEMU is efficiently handling multiple threads and system calls. - If you're seeing hangs or timeouts, the fact that both threads are waiting on system calls could indicate a resource bottleneck (e.g., I/O, network, or disk). - The use of futexes suggests that QEMU is leveraging fine-grained locking for concurrency. Let me know if you'd like further clarification or analysis!