Hi Stan,
Currently Intel 5000 series MCH supports two types of power
saving: putting memory into low power state and shutting down unused
memory.
For the first type of power saving by putting memory into low
power state, it's really based on memory controller thermal protection
mechanism and works as below. When the entire system is predicted to be
idle for a relative long time, the driver will trigger hardware thermal
protection mechanism to throttle memory access requests which has
similar effection of frequence deduction. When system is in thermal
protection state, all memory contents are preserved and system can
access all memory but with reduced bandwidth and power consumption. When
system wakes up from idle, driver will restore normal memory operation
mode. The transition time is about several microseconds. This kind of
memory power saving will operate on the whole memory instead part of
them and is feature of Intel 5000 series MCH. Future memory controller
may support this type of power saving by hardware automatically without
software's assistance.
The second type of memory power saving mechanism is shutting
down unused memory components. All memory contents will get lost after
shutdown so it needs OS'es help to free up all memory in a specific
range before shutting down corresponding memory components. To enable
this type of power saving, there's much more work needed to be done. OS
needs to monitor memory usage and provide mechanism to free/move memory
in a specific range, this ability may also be needed by memory hotplug.
It could provide full power management on memory components conforming
to Solaris PM system by adopting this type of memory power saving
mechanism. It will get more important and useful in NUMA system, some
nodes with CPU and memory controller may be entirely shut down when
system is under low pressure.
To sum up, the first type memory power saving mechanism is much
more ease to implement and will take effect when entire system is idle.
The second type memory power saving mechanism could provide us a cpupm
like "mempm" with full power management capability in current and future
systems, but with much much more work.
Stan Studzinski <mailto:stan.studzinski at sun.com> wrote:
> On Wed, 12 Mar 2008, Liu, Jiang wrote:
>
>> / All,
> />/ I would like to propose a project to enable FB-DIMM idle power
> />/ saving on Intel 5000P/5000V/5000Z MCH chipsets.
> />/ Intel 5000 series MCH chipsets have a thermal protection
> />/ mechanism which can be used to reduce FB-DIMM power consumption
> when />/ system is idle. This power saving mechanism has been proven
> to be very />/ useful in real IDC. On the other hand, platforms based
> on Intel 5000 />/ series MCH will continue to ship until the end of
> 2009 plus 4-5 years' />/ lifetime. So enabling FB-DIMM power saving
> feature can make systems />/ based on 5000 series MCH more power
> efficient and save money for />/ customers.
> />/ Any thoughts or suggestions?
>
> Hi Gerry,
>
> From your proposal it sounds like FB-DIMM power consumption can
> be reduced when the system is idle.
> How does this work? From your previous emails this feature applies
> to whole memory which means that one can not turnoff specified chunks
> of memory. Is this correct?
> Does this mean that for memory in a "lower power state" (or LPS) all
> data is preserved?.
> From what I understand so far is that if system tries to access LPS
> memory the software has to enable memory (via register) and then
> memory can be accessed again.
>
> When the system is idle and the memory is off we can't execute code
> from RAM?
>
> Stan
>
> />/
> />/ Liu Jiang (Gerry)
> />/ Senior Software Engineer
> />/ OpenSolaris, OTC
> />/ Tel: (8610)82611515-1643
> />/ iNet: 8758-1643
> /
