CPU frequency goes to minimum appx. 40 seconds after booting/resuming

Question

I'm on an Acer laptop with an Intel i7-4710HQ, which is nominally clocked at 2.50 GHz/goes to 3.50 GHz with turbo boost. As soon as I can run turbostat after booting or doing a suspend/resume, it reports Bzy_MHz near enough to nominal values:

 Core     CPU Avg_MHz   %Busy Bzy_MHz TSC_MHz
   -       -     392   11.42    3436    2503
   0       0     151    4.49    3353    2504
   0       1      67    1.99    3340    2504
   1       2      96    2.84    3366    2504
   1       3     175    5.22    3350    2504
   2       4     105    3.14    3349    2504
   2       5      81    2.43    3322    2504
   3       6      46    1.38    3333    2504
   3       7    2419   70.03    3453    2496

However, this drops to 800 MHz around 40 seconds later:

 Core     CPU Avg_MHz   %Busy Bzy_MHz TSC_MHz
   -       -       8    1.01     798    2493
   0       0      12    1.55     798    2493
   0       1       1    0.16     800    2493
   1       2      21    2.65     798    2493
   1       3       9    1.11     798    2493
   2       4      15    1.84     798    2493
   2       5       1    0.08     797    2493
   3       6       3    0.40     798    2493
   3       7       2    0.29     798    2493

It's not represented here, but this persists when I load the CPU. Doing a suspend and resume or a reboot brings the frequency back up for another 40 seconds or so. The drop happens typically at 40-45 seconds but sometimes as late as 50 seconds after booting/resuming.

For reference, here is (part of) the output of cpufreq-info: (the output is identical for the other CPUs, of which there are 7)

analyzing CPU 0:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 0.97 ms.
  hardware limits: 800 MHz - 3.50 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 800 MHz and 3.50 GHz.
                  The governor "performance" may decide which speed to use
                  within this range.
  current CPU frequency is 800 MHz.

And of lscpu:

Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                8
On-line CPU(s) list:   0-7
Thread(s) per core:    2
Core(s) per socket:    4
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 60
Stepping:              3
CPU MHz:               800.097
BogoMIPS:              4988.66
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              6144K
NUMA node0 CPU(s):     0-7

rdmsr gives a value of 8 for register 0x19a. This is true before and after the CPU frequency drops. (Using wrmsr to set it to 0, either before or after the frequency drops, does not affect the behaviour.)

The information you have seen was generated while I was running intel_pstate. However, disabling this at boot (such that cpufreq-info reports using the acpi_cpufreq driver) does not affect the behaviour. Setting processor.ignore_ppc=1 also does not affect the behaviour.

I'm already using the performance governor. Changing scaling_min_freq does not affect the behaviour. The behaviour is the same whether I am plugged in w/ battery charging or on battery only.

I don't typically observe a temperature above 70 degrees C, and in a number of test runs the temperature has been stable at near 65 degrees for each core when the frequency drops.

Update with requested information:

rdmsr --bitfield 15:8 -d -a 0x198 gives 33 for all CPUs after resume, and drops to 8 when the frequency drops.

rdmsr --bitfield 15:8 -d -a 0x199 gives 35 for all CPUs after resume and does not change when the frequency drops.

grep . /sys/devices/system/cpu/intel_pstate/* (after drop):

/sys/devices/system/cpu/intel_pstate/max_perf_pct:100
/sys/devices/system/cpu/intel_pstate/min_perf_pct:100
/sys/devices/system/cpu/intel_pstate/no_turbo:0

grep . /sys/devices/system/cpu/cpu0/cpufreq/* (after drop):

/sys/devices/system/cpu/cpu0/cpufreq/affected_cpus:0
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq:800000
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq:3500000
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq:800000
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency:4294967295
/sys/devices/system/cpu/cpu0/cpufreq/related_cpus:0
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors:performance powersave
/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq:800000
/sys/devices/system/cpu/cpu0/cpufreq/scaling_driver:intel_pstate
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor:performance
/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq:3500000
/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq:800000
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed:<unsupported>

All of these were obtained with the CPU loaded.