Cpuspeed Govenors on Intel Westmere/Sandy-Bridge CPUs

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I have been looking into the pros and cons of the "performance" and "ondemand" cpuspeed govenors on some of our machine types. On all machines I can see a measurable performance drop-off when using ondemand.

However, when I look at the power draw from the relevant lights out management cards I can't see any power saving to be found on Westmere or Sandy-Bridge CPU.

My testing setup...

Machine 1 - HP ProLiant DL385 G6, 2x 2.4GHz 6-core AMD Opteron 2431, running RHEL 6
Machine 2 - Fujitsu Primergy RX600 S6, 4x 2.67GHz 8-core Intel E7-8837, running RHEL 5
Machine 3 - HP Proliant DL380p G8, 1x 2.4GHz 4-core Intel E5-2609, running RHEL 6

Reported energy usage from LOM GUI under 0% CPU load

         ondemand       performance

Machine 1 160W 236W
Machine 2 624W 624W
Machine 3 64W 64W

I can see that all three machines do appear to be throttling down the CPU speed as I would expect via /proc/cpuinfo. Machines 2 & 3 only seem to be throttling down to 50% of their rated speed compared to the older AMD one that drops to 800MHz.

I switched between govenors by editing /etc/sysconfig/cpuspeed and then issuing a '/etc/init.d/cpuspeed restart'. I confirmed the govenor change by looking at the scaling_govenor values found under /sys/devices/system/cpu

Am I missing something or is there no point in using the ondemand govenor on these latest CPUs?

gr

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