Performance Monitoring & Tuning Flashcards

Which command from the sysstat suite collects and reports historical system activity data on a scheduled basis?

Answer: sadc

sadc (System Activity Data Collector) is the backend daemon that records data later read by sar.

What does the 'b' column in vmstat output represent?

Answer: Number of processes blocked waiting for I/O or other resources

The 'b' column in vmstat shows processes in uninterruptible sleep, typically waiting on I/O.

Which command pins a process or command to specific CPU cores using a CPU affinity mask?

Answer: taskset

taskset sets or retrieves a process's CPU affinity, controlling which cores it may run on.

What does 'iowait' percentage in top or mpstat specifically measure?

Answer: CPU time spent idle while at least one I/O request was outstanding

iowait is CPU idle time that occurs when the system has pending disk I/O, indicating potential I/O saturation.

Which /sys path allows you to change the I/O scheduler for a specific block device at runtime?

Answer: /sys/block//queue/scheduler

Writing a scheduler name (e.g., 'mq-deadline') to /sys/block//queue/scheduler changes it live.

What is the primary advantage of the 'BFQ' (Budget Fair Queuing) I/O scheduler for desktop workloads?

Answer: It allocates I/O bandwidth proportionally to processes, reducing latency for interactive applications

BFQ provides per-process fair I/O budgeting, improving responsiveness for interactive tasks.

Which command reports per-process disk I/O statistics including reads, writes, and I/O delay?

Answer: pidstat -d

pidstat -d shows disk I/O statistics broken down by process ID.