This document evaluates the cost and energy reduction potential of using ARM-based servers instead of Xeon servers. It finds that ARM Cortex A9 processors can be up to 11 times more energy efficient for web serving workloads based on benchmarks. This increased efficiency could enable total cost savings for data centers of up to 12.7% according to models. ARM servers were found to be 3.6 times more efficient for SIP proxy workloads and 2.9 times for more demanding web service workloads, enabling potential cost savings of 10% and 9%, respectively.

1. Cost and Energy Reduction Evaluation
for ARM Based Web Servers
Olle Svanfeldt-Winter, Sébastien Lafond, Johan Lilius
Sébastien Lafond
sebastien.lafond@abo.fi
13.12.2011 Åbo Akademi University - Department of Information Technologies 1

2. Outlines
Motivations
Energy consumption
Total energy consumption
Energy propositional computing
Data Centers Costs
Evaluated HW
Benchmarks
Results
Conclusion
13.12.2011 Åbo Akademi University - Department of Information Technologies 2

3. Motivations
Energy consumption of data centers is both an
economical and environmental issue
– important impact on the possibility to construct or
expend data centres
– cooling infrastructures are expensive
Models for data centre costs exists
– It is possible to determine the relationship between the
total cost of a data center and the energy consumption of
its server
13.12.2011 Åbo Akademi University - Department of Information Technologies 3

4. Energy consumption
The two main metrics are:
TotalFacilityPower
– PUE = ITequipmentPower
1
– DCiE = ×100
PUE
Both express the energy efficient of the data center
But at the end the total energy consumption matters
– this is what you will pay for every month
– infrastructure design based on the maximum power
dissipation of the data center
13.12.2011 Åbo Akademi University - Department of Information Technologies 4

5. Total energy consumption
According to [1] the processors in a typical server
contributed to:
– 45% of the total power dissipation at peak
performance
– 27% when idle
Power dissipation is application specific, but on
average the dissipation is 72% of the peak power
Google server containers are reported to house
1160 servers and dissipate 250KW each.
[1] L. Barroso and U. Holzle, “The case for energy-proportional computing,” Computer,
vol. 40, no. 12, pp. 33–37, December 2007.
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6. Energy propositional computing
Ideally the energy consumption of data centers
should be proportional to the required performance
– this is unfortunately far from being true
– energy efficiency is best at peak performance
– however typical servers operate most of
the time at 10 to 50% of their capacity
Using low-end and cheaper processors might be an
answer for better energy proportionality
– increase the granularity of power management steps
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7. Data Centers Costs
Based on Hamilton analysis [1,2]
• $0,07 per KWh
• 80% average load usage
• 50k servers
• 165 W per server
• 5% cost of money
• 10 year amortization time
• 4 year amortization time for the network
• 3 year amortization time for the server
[1] J. Hamilton, “Cooperative expendable micro-slice servers (cems): Low cost, low power servers for internet-scale
services,” in Proceedings of CIDR 09, January 2009.
[2] “Overall data center costs. http://perspectives.mvdirona.com/2010/09/18/overalldatacentercosts.aspx,” James
Hamilton, September 2010
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8. Evaluated HW
Versatile Express
– Quad-core Cortex A9
– 1GB DDR2
– 400Mhz
Tegra 250
– Dual-core Cortex-A9
– 1GB DDR2
– 1Ghz
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9. Benchmarks
Autobench and Apache 2 HTTP server
– static web pages
SPECweb2005
– more demanding web services
Erlang
– micro benchmarks
– real world SIP proxy
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10. Results
Apache
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11. Results
SPECweb2005
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12. Results
Erlang
Calls per dissipated Watt
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13. Conclusion
The performance of 2 ARMv7 based ARM cortex-A9
was measured and evaluated and compared to Xeon
processors
Measurements show that the Cortex A9 can be up
to
– 11 times more efficient with the Apache server
• Enabling a 12,7% total cost saving
– 3.6 times more efficient with Erlang base SIP proxy
• Enabling a 10% total cost saving
– 2.9 times mote efficient with the SPECweb2005
• Enabling a 9% total cost saving
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14. Questions ?
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