AN3129

IRQ latency measurement

Doc ID 16927 Rev 1

5/12

4

IRQ latency measurement

The latency measurement module is a Linux kernel module (LKM) available as part of the

STLinux SPEAr BSP release kernel code. This module can be statically linked with the

kernel at the time of the build.

This module is useful for measuring the IRQ or FIQ latency in a running system. The

statistics collected are:

●

Maximum latency (in microseconds)

●

Minimum latencies (in microseconds)

●

Total number of samples captured

●

Frequency distribution of IRQ handling latency in range [0-200] microseconds

Figure 3.

Linux Kernel IRQ latency measurement module

To see above modes in the kernel source directory:

1.

Run make menuconfig.

2.

Then navigate to ‘System Type’->’SPEAr Interrupt Latency Test’]

The source code of the latency measurement module is available in the STLinux SPEAr

BSP Linux kernel source code.

The file location is: arch/arm/plat-spear/latency_test.c

You can use this module as a starting point for writing a new FIQ handler.

4.1

Using the latency measurement module

The latency test module exchanges configurable parameters and measured results through

Linux sysfs filesystem.