Features/LatencyPolicy

= Power Management Latency Policy =

Summary
Power management modes save a ton of power, but also increase the time it takes to respond to interrupts. Most users don't care as these delays a typically in the μs range, but you might if you're on a server processing financial data.

Owner

 * Name: Richard Hughes

Current status

 * Targeted release:  Fedora 10
 * Last updated: (2008-07-15)
 * Percentage of completion: 70%

Detailed Description
Latency is the time delay between the moment something is initiated, and the moment one of its effects begins or becomes detectable. Most users don't care as these delays a typically in the μs and low ms range, but you might if you're on a server processing financial data or low latency set top box.

latency-policy is a set of extendible scripts that allow an admin to set a global preferred latency value, which is used to enable or disable different power management modes like ALPM, ASPM, ALSA powersave and ondemand.

Benefit to Fedora
Increased configurability for admins who care about this latency stuff. For users, we can configure by default more aggressive power saving modes with the ability to turn them off temporarily if they cause regressions.

Scope
Requires packaging and installing by default the latency-policy package.

Test Plan

 * 1) Install latency-policy
 * 2) Boot computer, observe correct modes are set for desired latency

User Experience

 * 1) Users should have aggressive power saving on by default, without understanding all the insane names and how they might affect the system "sluggisness".

Dependencies

 * kernel-2.6.26

Contingency Plan

 * Don't ship latency-policy by default

Documentation

 * http://people.freedesktop.org/~hughsient/releases/

Release Notes
Fedora 10 will include the latency-policy package, which enables more aggressive power management modes by default. It also enables admins to trivially change the latency metric or enable and disable different power saving modes manually.

Comments and Discussion
See Talk:Features/LatencyPolicy