Книга: Embedded Linux Primer: A Practical, Real-World Approach

17.4.3. Debug Wakeup Timing

17.4.3. Debug Wakeup Timing

To enable wakeup timing, enable CONFIG_WAKEUP_TIMING in the kernel configuration. This debug option enables measurement of the time taken from waking up a high-priority process to when it is scheduled on a CPU. Using it is simple. When configured, measurement is disabled. To enable the measurement, do the following as root:

# echo '0' >/proc/sys/kernel/preempt_max_latency

When this /proc file is set to zero, each successive maximum wakeup timing result is written to this file. To read the current maximum, simply display the value:

# cat /proc/sys/kernel/preempt_max_latency
84

As long as any of the latency-measurement modes are enabled in the kernel configuration, preempt_max_latency will always be updated with the maximum latency value. It cannot be disabled. Writing 0 to this /proc variable simply resets the maximum to zero to restart the cumulative measurement.

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