SKL only - igt@i915_pm_rc6_residency@rc6-idle - fail - Exceeded energy expectations for single busy wait load

https://intel-gfx-ci.01.org/tree/drm-tip/IGT_5535/shard-skl8/igt@i915_pm_rc6_residency@rc6-idle.html

Starting subtest: rc6-idle
(i915_pm_rc6_residency:1154) CRITICAL: Test assertion failure function rc6_idle, file ../tests/i915/i915_pm_rc6_residency.c:401:
(i915_pm_rc6_residency:1154) CRITICAL: Failed assertion: 2 * phases[2].power - phases[0].power <= phases[1].power
(i915_pm_rc6_residency:1154) CRITICAL: Exceeded energy expectations for single busy wait load
Used 3.3mW, min 2.8mW, max 3.3mW, expected less than 3.1mW
Subtest rc6-idle failed.

(i915_pm_rc6_residency:1154) DEBUG: slept=3000820515 perf=3000932422, rc6=3000934435
(i915_pm_rc6_residency:1154) INFO: Total energy used while idle: 0.0mJ
(i915_pm_rc6_residency:1154) DEBUG: normal: slept=3000834697 perf=3000991864, cycles=8, rc6=2969392957
(i915_pm_rc6_residency:1154) INFO: Total energy used for normal: 8.4mJ (2.8mW)
(i915_pm_rc6_residency:1154) DEBUG: boost: slept=3000830043 perf=3000978781, cycles=8, rc6=2965184714
(i915_pm_rc6_residency:1154) INFO: Total energy used for boost: 9.9mJ (3.3mW)
(i915_pm_rc6_residency:1154) DEBUG: once: slept=3000688783 perf=3000827640, cycles=9, rc6=2961637448
(i915_pm_rc6_residency:1154) INFO: Total energy used for once: 9.8mJ (3.3mW)