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dmaLatencyTuned

Power consumption is based on C-States. http://pm-blog.yarda.eu/2011/10/deeper-c-states-and-increased-latency.html

You can adjust kernel response time - and accordingly CPU consumption - by writing to /dev/cpu_dma_latency

Why this tool ?

By experience, default timings are too aggressive in current kernel, and CPU goes to C6-state too often, leading to a less responsive server. I personnally found a 40% difference performance on some benchmarks ! I wrote this tool after exposing my problem on kernel mailing list here : http://comments.gmane.org/gmane.linux.kernel/1425277

Performance comparison

See for yourself : Benchmark

How it works

This tool monitors /proc/stat and write to this file to get the most effective value :

  • if CPU is idle, allow C6/C7, and then change based on load.
  • When CPU is heavily used, stay in C0

To see C-States / dma_latency value relationship :

cat /sys/devices/system/cpu/cpu0/cpuidle/state*/{name,latency}

Future

  • Rewrite this tool in pure C
  • Tune values