Edge vs. Level triggered logic

A brief explanation of "edge triggered" and "level triggered" logic.

Transcript

1. Google Cloud Platform Kubernetes: Edge vs. Level Triggered Logic Tim Hockin <thockin@google.com> Principal Software Engineer @thockin
2. Google Cloud Platform Once upon a time there was hardware When the hardware needed attention, it would signal the CPU == “interrupt” Interrupts used be a literal wire from the device to the CPU
3. Google Cloud Platform Device CPU interrupt line
4. Google Cloud Platform The device can change the voltage on the wire The CPU can detect changes in voltage
5. Google Cloud Platform low voltage high voltage edge edge
6. Google Cloud Platform Simple: the device “pulses” the interrupt line The CPU reacts This is “edge triggered”
7. Google Cloud Platform Device CPU
8. Google Cloud Platform Problem: what happens if the CPU doesn’t detect a pulse? The interrupt doesn’t get serviced!
9. Google Cloud Platform low voltage high voltage level level
10. Google Cloud Platform The device can change the voltage and keep it there until the interrupt is serviced The CPU can’t miss edges The device can “stack” interrupt reasons - leave the voltage until all reasons are ACK’ed This is “level triggered”
11. Google Cloud Platform Device CPU
12. Google Cloud Platform What does this mean for Kubernetes? State is more useful than events Level-driven software is about asserting state Clients can check and re-check state at any time This is the heart of Kubernetes’ controller model