| # CPU Samples |
| |
| The [Harvester](README.md) gathers a collection of CPU samples from each CPU on |
| the device. This document describes how the data is labelled and what the values |
| represent. |
| |
| ##### Dockyard Paths |
| |
| The path to each sample will include "cpu", the processor index, and the sample |
| name: e.g. "cpu:0:busy_time". |
| |
| ### Samples |
| |
| Data collected by the Harvester along with timestamp and a Dockyard Path is |
| called a Sample. The following sections describe CPU samples collected. They are |
| grouped in four broad categories. |
| |
| #### Load |
| |
| The busy and idle times are complementary. The busy time is derived from the |
| idle time. |
| |
| ##### cpu:count |
| The number of main CPUs. For the "cpu:\*:" sample paths the "\*" will be a |
| number from 0 to (cpu:count - 1). |
| |
| ##### cpu:\*:busy_time |
| The total accumulated time this processor has been busy. |
| |
| ##### cpu:\*:idle_time |
| The total accumulated time this processor was not doing work (not running any |
| threads). |
| |
| #### Kernel scheduler counters |
| |
| The scheduler schedules threads. It determines which thread a given CPU should |
| be running. |
| |
| ##### cpu:\*:reschedules |
| How many potential context_switches occurred. All context_switches are |
| preceded by a reschedule, but not all reschedules result in a context_switch. |
| |
| ##### cpu:\*:context_switches |
| How many thread switches have occurred. A high value may indicate threads |
| are thrashing (spending an inordinate amount of time switching places rather |
| than doing work). |
| |
| ##### cpu:\*:meaningful_irq_preempts |
| How many thread preemptions have occurred due to an interrupt (irq) while the |
| CPU is not idle. If the thread is idle the interrupt is not considered |
| meaningful and is not tracked here. |
| |
| ##### cpu:\*:preempts |
| How many thread preemptions have occurred. (Not currently used). |
| |
| ##### cpu:\*:yields |
| How many times a thread has yielded its use of a processor to allow another |
| thread to execute. |
| |
| #### CPU level interrupts and exceptions |
| |
| An interrupt causes the current flow of a thread to be "interrupted". The thread |
| is stopped, the state is preserved (so it can be resumed) and the processor |
| executes an interrupt handler (function). |
| |
| ##### cpu:\*:external_hardware_interrupts |
| External hardware interrupts indicate a signal or event happening outside of |
| the machine. Common examples are serial input, or a physical button like a |
| volume up or down button. Does not include timer or inter-processor interrupts. |
| |
| ##### cpu:\*:timer_interrupts |
| A timer interrupt occurs when a "clock" (or some kind of time keeping device) |
| creates an interrupt. |
| |
| ##### cpu:\*:timer_callbacks |
| How many times a function (callback) has been called due to a timer. Each time |
| a timer interrupt occurs, zero-to-many timer callbacks may be called. |
| |
| ##### cpu:\*:syscalls |
| How many system (kernel) API calls have been made. |
| |
| #### Inter-processor interrupts |
| |
| An inter-processor interrupt occurs when a processor signals another processor. |
| |
| ##### cpu:\*:reschedule_ipis |
| The count of times the scheduler (running on some CPU) has requested a |
| schedule change (waking up another CPU). |
| |
| ##### cpu:\*:generic_ipis |
| The count of inter-process interrupts that were not a schedule change (tracked |
| as reschedule_ipis), ipi interrupt (untracked), or ipi halt (untracked). |
| |
