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This is not a new tunable, it's been in the kernel since the earliest RHEL6 releases.

That being said, I'm not an expert on it.  It went in for Bug 585330 - ["RHEL6] Fix performance issue with ondemand governor" over 3 years ago.  Rik van Riel owned that bug.

Well, anyway, to the best of my understanding it makes IO count as "CPU busy" so that the cpu doesn't go into a power saving state while IO is happening, thus keeping IO perf from dropping.

This patch added the tunable and offers a brief description of what it does.

http://patchwork.usersys.redhat.com/patch/25156/

Note that the 6.6 flag has been removed because this bug can be completed asynchronously, not because it is nacked for the 6.6 timeframe.

The update is available on the Customer Portal:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/index.html#s-cpu-cpufreq

Closing the BZ.