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These options are listed under Memory Power Management in the Power Options on my laptop:

  • Backoff channel heat break tolerance
  • Consecutive time units to mark a page as cold
  • Backoff channel heat check interval
  • Backoff idle utility threshold
  • Backoff forced hot channel resume timeout
  • Time unit in 2^minutes for access pattern
  • Monitor short history
  • Monitor channel power history
  • Monitor long history
  • Free pages threshold to move pages out of pinned channel
  • PFNs query rate per node
  • Monitor check interval
  • Backoff frequency threshold
  • Backoff low utility threshold
  • Memory stats check interval
  • Pinned pages number above which to mark a channel as pinned
  • Maximum hot pages to put channel in low power state
  • Relocation rate per node
  • Backoff high utility threshold

Seeing this list of options makes me Speechless, so...

  • What does each option do in layman's terms?

  • How do I go about and fine-tune these settings?

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If your tech level at the scale of 1-10 is less then 8 (means you are not called by friends to fix their computers), you probably do not want to install this version. The build is not for laymans... it is for software developers to find compatibility issues in their software or hardware drivers. I am sure at the time of launch the tech writing experts will be summoned to review word choice, but generally speaking, you cannot get a layman to read "Windows Internals 5th edition" or get programmers to read "introduction to journalism". If you want to hear from developers, ask on stackoverflow. – Sheng Jiang 蒋晟 Sep 16 '11 at 19:22
@Sheng Jiang: I am a developer, so I'm up in the higher end; yet, this question is legitimate for Super User and has nothing to do with programming. The internet nor Windows Internals contains any reference to this as far as I can see from doing multiple different attempts; so, that's why I'm asking this here to see if someone else has way more experience, as in looking for the experts in the OS Internals niche which regards to configuring the power options. From that point, I'm a layman to low-level hardware memory settings but that doesn't make me a layman in general... – Tom Wijsman Sep 16 '11 at 20:00
You could be a great developer and not understand this. You'll want to talk to a device driver dev. I tried to understand this by asking my C dev friends and it was way over my head, so I'm not gonna try to type out what I just heard. – surfasb Sep 17 '11 at 0:02
I'll be surprised if these options end up in the shipping version of Windows 8 as anything more than registry edits. They've probably only been exposed for testing and will disappear as Microsoft or various hardware partners optimize the settings themselves. With that number of variables to deal with, I imagine you'll have a very hard time improving anything over the out of the box defaults once Windows 8 goes RTM. – afrazier Feb 24 '12 at 14:30
@frazier: With a good understanding of them, one could optimize a setting individually. Of course, good benchmarking would be required to see if it is an actual improvement. It's tricky, but for now I haven't found any information on them whatsoever. I guess they indeed slipped in by accident... – Tom Wijsman Feb 24 '12 at 17:41
up vote 4 down vote accepted

These options are intended for device and driver developers in particular. If in doubt do not touch as these values can dramatically affect your machine's performance in the negative direction. In general the default configuration will always be the most performant for your machine setup.

But to answer your questions specifically, here is a break down:

Backoff channel heat break tolerance - The amount of heat that is tolerated in a specific power channel before the channel is moved to "backoff" mode - i.e. turned off to avoid damage. (a power channel here is a device, although there may be more than one power channel per device). High values here can cause device damage and low values can cause devices to turn off during heavy use.

Consecutive time units to mark a page as cold - Length of time (in scheduler ticks) before a page in memory is marked as "old" and becomes eligable to be shuffled, paged-out or even deallocated by the kernel from underneath the driver. Lower numbers here can cause severe device performance penalties and higher numbers can cause devices to consume larger amounts of physical RAM than is necessary (slowing down the rest of the system slightly).

Backoff channel heat check interval - The number of scheduler ticks between checking the Backooff channel heat break tolerance timer. Higher numbers are more precise but take up more CPU time to perform the checks.

Backoff idle utility threshold - the number of scheduler ticks of no activity before a device is moved to the "idle" power mode. Higher numbers cause devices to turn off quicker when not in use.

Backoff forced hot channel resume timeout - the number of scheduler ticks after a device is disabled for being too hot before it is re-enabled.

Time unit in 2^minutes for access pattern - some value N in this field implies that every 2-to-the-power-N minutes the access-pattern device check is performed on the device. This check is a more complicated check to decide how the device is being used in order to select the next power state for the device.

Monitor short history - If set, causes the short history (verbose) log to be written to the event log. This is useful for debugging but causes additional disk access.

Monitor channel power history - If set causes power-channel power history to be recorded to the event log.

Monitor long history - If set causes the long history (statistical) log to be written to the event log.

Free pages threshold to move pages out of pinned channel - The number of free pages that a pinned channel has to have before it becomes "unpinned". This is to do with NUMA.

PFNs query rate per node - this is for NUMA/RAM configurations, are refers to the number of page frame number queries per node that occur for any given NUMA node. This is particularly important for multi-core and larger systems.

Monitor check interval - If set then various timer ticks are recorded to the event log.

Backoff frequency threshold - how often the "backoff" timer is checked.

Backoff low utility threshold - at what point of low usage the backoff timer is automatically fired in order to make use of system idle time.

Memory stats check interval - the number of scheduler ticks between checking memory statistics and writing them to the event log.

Pinned pages number above which to mark a channel as pinned - the number of pages that a channel needs to allocate before the channel becomes marked as a pinned channel (which gives it priority for certain actions).

Maximum hot pages to put channel in low power state - the maximum number of pages which are awaiting a driver response before the device is put into idle mode. This is important for network devices in order to get power gain out of throttling the device when packets are coming into the computer faster than the driver can process them.

Relocation rate per node - this is to do with NUMA access.

Backoff high utility threshold - the threshold of high utility before the backoff timer is queried.

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If you hover your mouse over the settings you get tooltip with description of each item. But for what they actually do you probably want to read the DDR3 standard or how Linux implements it.

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I'm going to look where these are stored at a later time and if these stored registry settings will be available in the released version I will try and read this; so, I can't accept your answer yet as I don't find it worth doing now but will follow-up in the future if it did answer my question. Thanks for mentioning where I might possible find details on this, would be interesting to learn about this; but I doubt I won't be able to make any performance improving change though... – Tom Wijsman Sep 19 '11 at 22:40

This is the best thing I could find as far as explanations on the Internet go. It's not very good though but I hope it helps at least a little bit:

The only options with (mostly unsatisfactory) explanations given are:

  • Backoff channel heat break tolerance. This option allows specifying the count that memory cooling channel trend break can tolerate.
  • Consecutive time units to mark a page as cold option allows specifying the time units to mark a page as cold.
  • Backoff channel heat check interval option is meant to allow specifying the time for checking a cold channel before it enters low power state.
  • Backoff idle utility threshold below which to consider backoff for idle.
  • Time unit for access pattern to select a time unit e.g. 3 minutes for access pattern.
  • Monitor short and long history options are meant to provide a time unit to monitor the short and long memory power history.
  • Monitor channel Power history to set a time for monitoring channel power history.

Others don't have any explanation.

Note: The current Windows 8 build is quite raw and changing memory related power options can cause system instability. Use any of the above mentioned memory power management settings at your own risk.

As afrazier says, they're very likely only available for testing. When Windows 8 will be released, they will very likely be replaced with smaller number of simpler options (understandable to regular users) or removed completely. Microsoft can't afford to make these power-user options available to general public and risk burning computers of customers unnecessarily.

PS: Please mention in your question that you're using Windows 8 Preview (and which version/build). For a moment I thought you're asking about some bloatware installed by your laptop manufacturer on Windows 7 or earlier version.

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These are the same explanations as when I hover the options. My question is properly tagged. – Tom Wijsman Feb 26 '12 at 18:02

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