5 Replies Latest reply on Oct 4, 2016 11:27 AM by Intel Corporation

    Turbo boost when all cores are busy?

    dbb

      Hi all,

       

      I see an unexpected (to me) behavior on an Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz.

       

      If I disable turbo boost and set the performance governor with intel_pstate on a recent Linux kernel, the p-state is fixed at 2.3GHz, which is what I expect.

       

      if I enable turbo and keep all cores busy with a tight loop doing some math, then the pstate appears to be 2.8GHz (and the performance I measure corresponds); this is unexpected to me.

       

      I thought that the maximum p-state with all cores busy would not change by enabling and disabling turbo boost.

      Why would there be some all-cores-busy turbo frequencies above the nominal processor frequency?

       

      My problem is that I need to take some measurements and I would like to configure the system to stay at the maximum p-state regardless of load.

      Disabling turbo boost and setting the performance governor is the way I used to do this, but it seems that I am leaving some performance on the table that way, because I get 2.3GHz instead of the 2.8GHz that I get with turbo boost enabled.