Almost whole my question is in subject. Question is simple and straight forward.
Why reference frequency might be significantly lower ( ~13% ) than thread frequency on CPU with SKU without Turbo.
Package CPU_CLK_UNHALTED.REF_TSC CPU_CLK_UNHALTED.THREAD
package_0 350,845,000,000 398,688,400,000
CPU: Intel(R) Xeon(R) CPU E5-2407 0 @ 2.20GHz.
SMT (Hyper-threading) is disabled
My ideas are limited to two cases, either something wrong with VTune or PMU. Are there any other possibilities?
If I understood it properly CPU_CLK_UNHALTED.THREAD could have spent less time in halt state hence its counter value is higher.
Partial info is available in this thread https://software.intel.com/en-us/forums/topic/285232
Both counters are collected for the same conditions, so from my point of view it would be strange if one counter would observe by 13% more unhalted state than another.
Collection is run with target type "profile system" so it global and includes execution of whole SW stack.
Accordingly to this page http://ark.intel.com/products/64614 Turbo Boost isn't available for the SKU E5-2407 (Sandy Bridge). There is nothing to disable.
Yes, counters were collected simultaneously with VTune 2013 U14