trace-analysis: Скилл для анализа трассировок и связей

--- name: trace-analysis description: Skill for analyzing trace files and finding hard causal links across threads and processes (using waker_utid). --- ## Skill: Trace Analysis for Blocked Threads When analyzing traces for UI jank or blocked threads (e.g., monitor contention on main thread): 1. **Don't just look at the ancestors of a slice**: Looking at ancestors only shows the calling hierarchy on that thread. It might lead to dead ends or vague links if the callback was posted or triggered by another event loop. 1. **Follow the 'Woken By' or 'Waking' metadata**: Look at the 'Running' or 'Runnable' task on the timeline to inspect what event or thread woke it up or sent work to it. This bridges cross-thread and async gaps. In SQL queries, utilize the `waker_utid` and `waker_id` columns in the `thread_state` table to find the hard waker thread that moved the target from a sleeping to a runnable state. 1. **Look at syscalls to understand why a thread is not runnable**: If a thread is listed as `Sleeping` or `Blocked` (and not `Runnable`), look at recorded **syscalls** (such as `SYS_futex`) to understand what operation or system lock it was waiting for. This adds context on what exact kernel blocker stalled the thread. 1. **Trace cross-process flows (IPC/Binder)**: If a thread was woken by `system_server` or another process (like Play Store's `com.android.vending`), find out what service or operation was being called or completed (e.g. searching for `unbindServiceLocked` or `onAppUpdateInfo` in `slice` or `args` table). Using `waker_utid` to locate the waking thread allows identifying the exact operation handle on that waker thread, creating a causal chain across processes instead of relying on luck or timing estimates. 1. **Identify the chain of events**: Chrome -> Play Core library -> System Server (handling connection or binder completion) -> Event handled by background vs UI thread. This gives context on why a shared lock was taken and held synchronously. This approach avoids getting stuck in opaque library calls and allows tracking complete cross-process flows.