If you are Facebook and its 3 am on the East Coast of the United States you probably want to see your Servers in a low power state. This can save you money and make your server farms more ‘green’.
For DDR4 there are several ways to help reduce power consumption. They are:
- PreCharge Power Down
- Active Power Down
- Self Refresh
- Max Power Savings
- Reducing the frequency and stopping the clock
Key metrics here are not only the entering of these states but how long the memory stays in these states. In addition, additional power savings can be had if the clock is stopped during these power saving modes. Measurement and analysis of these events is key to maximum power savings. These metrics should show percentages (used cycles versus total cycles, or versus CKE qualified cycles) and be broken down on a Channel, Slot, and Rank basis. Another key metric would be the amount of seconds or cycles spent in each mode.
Why measure this?
- Cost Savings
- Memory Controller Code changes to increase power savings can be evaluated and verified
- Software efficiency: comparing two pieces of code that accomplish the same task functionally may be different with regards to power management.
The trade-off between Power Management and Performance is a never ending tug of war. If you want high performance you will pay for it with more power consumption. So some applications may be very aggressive with power management, like Facebook, but others, like high frequency traders want high performance. So burn baby burn!