Linux Timer

Low-Resolution Timer

Time Stamp: Jiffy

High-Resolution Timer

Time Stamp: Nanosecond
Clock Base: (1) Monotonic Clock (2) Real Time Clock

Dynamic Tick

Power Management

Objects for Time Management
Clock Sources
Clock Event Devices
Tick Devices

Linux IO Scheduler

The IO Schedulers

No-op Scheduler

This scheduler only implements request merging.

Anticipatory IO Scheduler (AS)

This scheduler implements request merging, a one-way elevator, read and write request batching, and attempts some anticipatory reads by holding off a bit after a read batch if it thinks a user is going to ask for more data.

This is optimised for the single disk systems.

Deadline Scheduler

The scheduler implements request merging, a one-way elevator, and imposes a deadline on all operations to prevent resource starvation.

Complete Fair Queueing Scheduler (CFQ)

The scheduler implements both request merging and the elevator, and attempts to give all users of a particular device the same number of IO requests over a particular time interval.

References:
Linux I/O Schedulers