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

17.4.5. Interrupt Off Timing

17.4.5. Interrupt Off Timing

To enable measurement of maximum interrupt off timing, configure your kernel with CRITICAL_IRQSOFF_TIMING enabled. This option measures time spent in critical sections with irqs disabled. This feature works in the same way as wakeup latency timing. 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 interrupt off timing result is written to this file. To read the current maximum, simply display the value:

# cat /proc/sys/kernel/preempt_max_latency
97

You will notice that the latency measurements for both wakeup latency and interrupt off latency are enabled and displayed using the same /proc file. This means, of course, that only one measurement can be configured at a time, or the results might not be valid. Because these measurements add significant runtime overhead, it isn't wise to enable them all at once anyway.

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