How does the DRAM caching work in MEMORY MODE?

[Daynes]

The memory mode of DCPMM uses DRAM to cache data from NVM. In this mode, can operating system see DRAM and how data is evicted? How does the DRAM caching work? Is that all done in hardware without the support of the OS?

If possible,I want to read more specific document,thanks!

[Emeth_O_Intel · Accepted solution]

Hi Daynes,

Thank you for contacting Intel® Optane™ DC Persistent Memory Community. 

In Memory Mode, the DRAM acts as a cache for the most frequently accessed data, while the Intel® Optane™ DC persistent memory provides large memory capacity.

Cache management operations are handled by the Intel® Xeon® Scalable processor’s integrated memory controller. When data is requested from memory, the memory controller first checks the DRAM cache, and if the data is present, the response latency is identical to DRAM. If the data is not in the DRAM cache, it is read from the Intel® Optane™ DC persistent memory with slightly longer latency.

The applications with consistent data retrieval patterns that the memory controller can predict will have a higher cache hit-rate, and should see its performance close to all-DRAM configurations, while workloads with highlyrandom data access over a wide address range may see some performance difference versus DRAM alone.

Also, data is volatile in Memory Mode; it will not be saved in the event of power loss.

Persistence is enabled in the second mode, called App Direct. 

Please if you have more questions do not hesitate and let me know and I will be more than happy to assist you.

Have a wonderful day.

Best regards,

Emeth O.

Intel Customer Support Technician

A Contingent Worker at Intel

[Daynes]

Hi Emeth, Thanks for your replying. Now that I can't control DRAM,if I use DCPMM in a virtual machine and configure it as MEMORY MODE,then I divide it into same size and multi-guest machine for different tenement,how can I guarantee that every tenement get same service?If one guest machine occupy a majority of space of DRAM,I think it's unfair to others.On the view of tenement,I pay same money but I obtain different performance(or different DRAM space). Is there any approach to manipulate DRAM? Daynes Intel Forums <supportreplies@intel.com> 于2019年12月4日周三 上午8:53写道：

[Emeth_O_Intel]

Hi Daynes,

Certainly, you can manipulate the Intel® Optane™ DC Persistent Memory and its capacity on your virtual environment.

VMware has the support for Intel® Optane™ DC persistent memory technology in “App-Direct” mode as well as “Memory” mode.

-Memory Mode:

VMware vSphere 6.5 Update 3 and 6.7 EP10 enable Intel® Optane™ DC Persistent Memory in “Memory” mode. 

VMware vSphere usage of Intel® Optane™ DC Persistent Memory in “Memory mode” can offer increased memory capacity and TCO improvements for relevant customer workloads. Initially, VMware will support “Memory” mode for limited use-cases in production deployments; such a deployment requires “explicit approval” from VMware for support. For more information, customers should contact their VMware representative.

However, I would like to share additional material that can help you to have a better understanding of this information and implementation: 

• Intel Optane DC Persistent Memory “Memory Mode” Virtualized Performance Study:

https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/performance/IntelOptaneDC-PMEM-memory-mode-perf.pdf

• PMEM Performance in vSphere 6.7 with Intel Optane DC Persistent Memory:

https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/performance/optane-dc-pmem-vsphere67-perf.pdf

• vSphere Persistent Memory in the vSphere Client:

https://www.youtube.com/watch?v=wI5G6RmtyLo

• Enhance your VMware VMs with Intel® Optane™ DC Persistent Memory | Intel Software: 

https://www.youtube.com/watch?v=bopbZXIB0-E

I hope you will find this information useful if you have more questions do not hesitate and let me know and I will be more than happy to assist you. 

Have a wonderful day.

Regards, 

Emeth O. 

Intel Customer Support Technician

A Contingent Worker at Intel

[Daynes]

Hi, Thanks for your replying. Is there any document or article describe the internal architecture?I have read some article only simply introduce the moudle in DCPMM,I'd like to know how the different moudle work together. Thanks. Intel Forums <supportreplies@intel.com> 于2019年12月4日周三 下午12:39写道：

[Emeth_O_Intel]

Hello,

Sure, let me double-check those details. Meanwhile, please check the document below and let me know if that information helps you.

https://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/optane-dc-persistent-memory-brief.pdf

Also, I would like to know if you have the possibility to provide me with more details of the internal specification that you are looking for in order to share the most accurate information.

I will highly appreciate the information, and I will be waiting for your outcome.

Have a wonderful day.

Best regards,

Emeth O.

Intel Customer Support Technician

A Contingent Worker at Intel

[Emeth_O_Intel]

Hello,

Thank you so much for your time.

This type of information can be provided only if you have an NDA (Non-disclosure agreement) with us.

By any chance do you this agreement?

Please let us know the information in order to proceed with the next step.

Have a wonderful day.

Regards,

Emeth O.

Intel Customer Support Technician

A Contingent Worker at Intel

[Emeth_O_Intel]

Hello,

I am following up on your case in order to verify if you still need help with this or any other assistance?

If so, please do not hesitate and let me know and I will be more than happy to assist you.

Best regards,

Emeth O.

Intel Customer Support Technician

A Contingent Worker at Intel

[Emeth_O_Intel]

Hello,

Due to the fact I have not seen any activity recently on this thread. I will proceed and close it.

Please if you have more questions do not hesitate and let us know and we will be more than happy to assist you.

Best regards,

Emeth O.

Intel Customer Support Technician

A Contingent Worker at Intel