UltraSPARC T1 - low power and the SWAP metric
By denissheahan on Dec 06, 2005
Low power was a key design point of the UltraSPARC T1 "Niagara" processor from the
ground up. Unlike other processors we took a simpler approach to the pipeline.
Avoiding deep and complex Out of Order pipelines reduced power consumption to less
than 5 watts per core. We have also made a smaller more efficient L2 cache which
is great for throughput and consumes a lot less power. The total power consumption
for the chip is typically less than 70 watts, about half of comparible x86 processors.
Soon after first silicon we started to measure the power drawn from
the processor and DDR memory. Using our Fireball bringup system we measured current
drawn by modifying the motherboard to attach test points to the memory and cpu voltage
regulators. The result was a very ugly setup involving an oscilliscope.
We ran an Oracle, Java and SAP workload on the box while taking the measurements.
None of these really drove the memory bandwidth, however, which has a theoretical max
of 25GB/s. WSe switched to to a memory exerciser that could push about 14GB/s to the
With the arrival of p0.0 Ontarios power measurement began in earnest. We used a number
of different memory exercisers. We took measurements with 8GB, 16GB and 32GB of
memory, with and without the PCI-X and PCI-E slots occupied. We also got a breakdown of
the power costs of the major components of the systems
- UltraSPARC T1 processor
- The DDR2 memory
- The 4 internal drives
- The fans
- The power supply efficiency
- The PCI-E and PCi-X slots
All these components make up the total system power.
These tests proved that even under the heaviest load the T2000 did not require the
initial 550 Watt power supplies we had specified. The most we measured was 340 Watts
fully loaded. A system running at 340 Watts is not in the efficient range of a
550 Watt supply. We decided to change the supply for a 450 Watt version which
is far more efficient the 340 Watt range. This represented a significant power saving.
This transition is currently progressing.
These initial T2000 power measurements were done with a Voltech AC Power Analyzer and
a Tektronix 745 Oscillascope after modifying the power cord. This mechanism
was not practical for most benchmark environments and did not scale as the number
of systems increased.
The solution we found was a simple Power Analyzer and Watt
meter called "Watts Up" which is available from Frys for about $70.
The meter is simple to use, it provides a socket for the T2000 power cable and
then the meter is plugged into the wall socket. You need two for the dual power
supplies of the T2000.
We bought a bunch of these meters and put two on each of the benchmark configurations
we were testing. We also used these meters on comparable Xeon systems. When running
a workload on a T2000 we often run it in parallel on a Xeon system and take
performance and power measurements for both.
All our measurements on T2000 showed huge reductions in power consumption and
heat generated relative to other servers. At the same time the performance on
the T2000 was better than these systems.
We were also presenting our technology to many customers at the time and were hearing
again and again how power an cooling were becoming a critical factor in server deployment.
Datacenters are at the limits of power be in and how hot air that
can be extracted. Racks can only be deployed half full or require a large amount
of space around them.
Customers were extremely interested in our low power technology. But we needed a
metric to combine performance with power consumption and the space taken up by
racks of systems in the datacenter
To achieve this Rick Hetherington, Distinguished Engineer and Chief Architect for the
UltraSPARC T1 and Mat Keep and his team developed the very elegant "Space, Watts and
Performance (SWaP)" metric calculated using the following formula
Space X Power Consumption
- Performance is any benchmark such as an industry standard or customer specific workload
- Space is the height of the server in rack units (RU)
- Power is the Watts consumed by the system either by specs or even better by measuring the draw
with a meter during the actual workload.
If two systems deliver the same throughput performance but one is 2RU and
draws only 300 Watts and the other 3RU and draws 800 Watts.
The SWap rating of the first would be 0.83 and the second 0.16.
The first system has a 5X advantage over the second when deployed in the datacenter.
For a full description see:
We really believe SWaP is good for customers as it shows the true cost of deploying
a system in a datacenter. We hope it becomes an industry standard approach to
power and space management in the datacenter.