[petsfed]

I think milliseconds overestimates by a few orders of magnitude, but non-real-time OSs really suffer for the intermediate IO stuff you expect in an embedded project (e.g. SPI, I2C, etc)

A long time ago, I was playing with Project Nerves on an Orange Pi running some flavor of debian. I was doing some I2C transaction (at 400 kHz, each bit is single-digit microseconds), and I ultimately had to have a re-attempt loop because the transaction would fail so often. I found a failure cutoff of 5 attempts was sufficient to keep going. I don't recall the failure rate, but basically, whenever a transaction failed, I'd have to reattempt 2-3 times before it eventually succeeded.

Meanwhile, on a bog-standard Arduino with an ATMega328P, I send the I2C traffic once, and unless the circuit is physically damaged, the transaction will succeed.