PAS: I/O Completion Emulator

Per-I/O binary feedback (UNDER/OVER) with four update rules — sleep misprediction reflected in app-perceived latency

I/O Completion Model

Each I/O:
  wake_time = sleep_duration + cs_overhead (δ)

  UNDER (device_time > wake_time):  app wakes before device completes
      app_latency  = device_time      (polls until done — correct latency)
      measured_io  = device_time

  OVER  (device_time ≤ wake_time):  device finishes while app sleeps
      app_latency  = wake_time        (wasted time — overslept)
      measured_io  = wake_time        (inflated!)

PAS uses only binary UNDER/OVER → no time-based feedback → no positive feedback loop

PAS Parameters

UP (A_up):

DN (A_dn):

Initial duration: μs

CS overhead (δ): μs

Trace Input

Preset:

Target duration: ms

Update Rules — SR(2nd-to-last, last)

UNDER, UNDER

adjust += UP
(accelerate increase)

UNDER, OVER

adjust = 1 − DN
(slight decrease)

OVER, UNDER

adjust = 1 + UP
(slight increase)

OVER, OVER

adjust −= DN
(accelerate decrease)

Avg App Latency

μs

Avg Device Time

μs

Latency Overhead

OVER Count

I/Os

Final Duration

μs

I/O 0 / 0 | 0.0 / 0.0 ms

I/O Completion Emulation

▬ Genuine Device Latency - - Requested Sleep ▬ Actual Sleep (sleep + δ) - - App-Perceived I/O Latency ■ Oversleep Penalty

Run emulation to see step-by-step log...