Limitations of RegMon

Limitations of RegMon's periodic Sampling

The maximal rate that the registers can be read through function calls is determined by the timing limitations within the Linux kernel and the processing duration of the function itself. Without going into all the details of the Linux timing capabilities and clock sources, we briefly summarize the two approaches for triggering periodic register reading.

In order to get higher sampling speed through more precise timer resolutions, we implemented RegMon based on the more recent high resolution timer subsystem (hr_timers). High resolution timers measure time at nanosecond-level resolution whereas standard Linux timers measure time at millisecond-level resolution.

The usage of the hr_timer subsystem depends on the hardware that needs to provide sufficient precise clock sources. The changes necessary to switch from using jiffies to hr_timers were straightforward to implement, and did not include any design changes. This way, we were able to increase the maximum sampling rate to 20.000 Hz. Similar to any possible change to RegMon monitoring parameter, the sampling rate can also be changed in an online fashion.