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Published byZoe Jacobs Modified over 7 years ago
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Matthew Garrett <mjg@redhat.com>
Going green with Linux Matthew Garrett
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Data centres are expensive
~3% of total US electrical consumption in 2010 ~15GW ~15 nuclear power stations
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Fixing infrastructure
On average, 1W of overhead for 1W of machine More efficient cooling systems More efficient power supplies
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Things are getting better!
0.2W of overhead per W of machine
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Flying car future Use waste heat to generate power
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Linux doesn't solve this
(Sorry)
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Things need to get a lot better...
High end hardware takes a lot of power 48 core system = ~350W at idle (with power management...)
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What can we do in software?
CPU power management dominates right now Modern x86 idles at ~0W Full power = ~20W per core (48 core system = 960W from CPUs alone!)
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Gettings CPUs to do less is key
An idle CPU is a cheap CPU Full package sleep means idle memory ~5W per stick of DDR3 at load, ~0.1W in self refresh Optimising CPU and memory use patterns makes a huge difference
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Idle CPU cores = idle CPU package
RAM
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One active core = active package
RAM
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Keeping idle is key
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Keeping idle is key
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Keeping idle is key
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Huge efforts to reduce wakeups
IPMI reworked Automounter moved to event driven model Application-level tuning Debug tools (powertop, systemtap)
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What are the numbers? At fully idle, Linux ~3% better than Windows
Things start getting interesting under load...
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(Illustrative results)
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(Illustrative results)
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Take home message From 10%-50% load, Linux significantly more power efficient Margin decreases up to 90%, equality reached at 100%
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Tweaking Linux behaviour
/sys/devices/system/cpu/sched_mc_power_savings
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RAM RAM
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One task RAM RAM
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Two tasks (sched_mc_power_savings = 0)
RAM RAM
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Two tasks (sched_mc_power_savings = 1)
RAM RAM
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Two tasks (sched_mc_power_savings = 2)
Process migrated RAM RAM
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Future trends Smarter scheduling More runtime memory power management
Increasing virtualisation as a power management strategy Power management of smaller system components
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Scheduling NUMA-aware migration
Consolidate active pages in smaller nodes Thermal-aware scheduling If a CPU is limited because of heat, don't use it
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Virtualisation Run virtualised rather than on real hardware
Consolidate guests on a smaller number of hosts Bring up hosts and migrate guests as demand increases (requires rapid guest migration)
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Load balancing Put backend machines to sleep
Wake when demand increases Reduced resume latency
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What are the tradeoffs? Focus has been on “free” power management
Is it really true?
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Well... Enterprise customers have enterprise demands
Sometimes that performance hit really does matter
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Latency can be a pain C-states inherently create latency
Some people really don't want latency There's an obvious conflict here
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pm_qos Simple solution is to let applications indicate their requirement pm_qos interface provides that
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Performance/power tradeoff
Not always the direction you'd think Intel's turbo mode depends on good idle PM (Benchmarks in the snow)
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Turning more off Marginal but measurable gains from caring about unused hardware Lots of machines have USB ports Many don't have anything in them...
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Genuinely user transparent
USB SD Firewire Audio?
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Focus on power management
Reducing power consumption reduces costs
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Focus on power management
Reducing power consumption reduces costs Reducing power consumption is good PR
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Focus on power management
Reducing power consumption reduces costs Reducing power consumption is good PR Reducing power consumption is common sense
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Questions?
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