White Paper - Power Management in Intel Architecture Servers

Demand Based Switching (DBS)
Introduction to DBS
DBS is a power-management technology developed by Intel, in which
the applied voltage and clock speed of a microprocessor are kept at
the minimum necessary levels for optimal performance of required
operations [1]. A microprocessor equipped with DBS operates at
a reduced voltage and clock speed until more processing power
is required. This is achieved by monitoring the processor’s use by
application-level workloads, reducing the CPU speed when it is running
idle while increasing it as the load increases. This technology was
introduced as Intel® SpeedStep® Technology in the server marketplace.
Typically a processor without DBS enabled always runs at the rated
speed and consumes corresponding power, independent of the
workload, even though the processor is capable of operating at
lower operating voltage and frequency combinations. So there is an
opportunity to reduce power when the workload levels are lower.
Internal Operation of DBS
Processor performance states (P-states) are a predefined set of
frequency and voltage combinations at which a given processor can
operate correctly, albeit at different performance levels. With higher
frequencies, one will experience faster performance, but to achieve
that the voltage also needs to be higher, which makes the processor
consume more power (power consumption is proportional to the
product of voltage squared and operating frequency).
The table inset in Figure 2 gives examples of a processor’s different
P-states. In the example, a savings of 35 watts occurs when the
processor runs at the lowest performance state. This can be achieved
by turning ON the DBS functionality on the BIOS Setup screen. This
state should always be selected during lean periods of application
usage. After enabling the DBS functionality, one can set policies in the
operating system (OS) to become effective at different workloads.
When application workloads change, it may change a processor’s
utilization, initiating a reduction in the processor voltage and clock
speed. In turn, the processor’s power consumption and corresponding
heat generation will drop, leading to cost savings in server power
consumption and data center cooling requirements.
Demand Based Switching
from P0 to P4 state
Terminate
No
Yes
Yes
Wait and check again1.4v 3.6 GHz 103 Watts
1.2v
2.8 GHz
68 Watts
Use DBS to downshift
voltage for the processor
Reduction in voltage
in-turn reduces clock-speed
Reduction in voltage and
clock speed reduces the
heat generated
Cooling needs are reduced
enabling cost reduction in
data centers
Is DBS
enabled?
Is the workload
(processor utilization)
reduced?
Example power-states
Power
State
P0
P1
P2
P3
P4
1.4v
1.35v
1.3v
1.25v
1.2v
3.6 GHz
3.4 GHz
3.2 GHz
3.0 GHz
2.8 GHz
103 Watts
94 Watts
85 Watts
76 Watts
68 Watts
FrequencyVoltage
Heat
Generated
Figure 2. Demand Based Switching leading to CPU power reduction�
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White Paper: Power Management in Intel® Architecture Servers