Mismatch in frequencies reported between sysfs and perf PMU

From original issue reported by ashwin.kumar.kulkarni@intel.com:

Frequencies reported by sysfs do not match those reported by PMU on ATSM.

Freq reported by sysfs can be seen as follows:

watch -n 0.1 'cat /sys/class/drm/card0/gt/gt0/rps_act_freq_mhz'

Similarly PMU reported frequencies can be seen using a command such as:

sudo ./perf stat -e i915_0000_4d_00.0/actual-frequency/ -I 1000

Or by running intel-gpu-top.

The mismatch in freq reported by sysfs and PMU can be seen in the attached png.