[Bug 108700] New: 2x Media CPU power usage, or 15% perf drop when CPU bound GPU use-case is TDP limited

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108700

            Bug ID: 108700
           Summary: 2x Media CPU power usage, or 15% perf drop when CPU
                    bound GPU use-case is TDP limited
           Product: DRI
           Version: DRI git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: eero.t.tamminen at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org
     i915 platform: CFL, KBL, SKL

Created attachment 142419
  --> https://bugs.freedesktop.org/attachment.cgi?id=142419&action=edit
parameter file for sample_media_transcode

Test setup:
* Ubuntu 18.04
* git head build of drm-tip kernel
* git head build of Mesa & X and their main deps
* git head build of Intel MediaSDK and their main dependencies

Good drm-tip version:
a4e9f377a9: 2018-11-03 01:29:29: drm-tip: 2018y-11m-03d-01h-28m-29s UTC
integration manifest

Bad drm-tip version:
1a4a6dafa1: 2018-11-05 16:07:52: drm-tip: 2018y-11m-05d-16h-07m-05s UTC
integration manifest

Test-case 1:
* Run (mostly) CPU bound GfxBench v4 Driver2 test

Test-case 2:
* Run MediaSDK provided tool with the attached parameter file (does 50 streams
which lower H264 video frame & bit rates, size and adds filtering):
  sample_multi_transcode -par inputs.par
* Sum FPS of all streams together

Outcome on HW that is TDP limited:
* Test-case 1 performance drops 15%
* Test-case 2 performance drops 5%
* Performance of other CPU bound GPU tests regress also, but less

Outcome on HW that isn't TDP limited:
* RAPL reports marginally larger CPU power consumption for test-case 1
* RAPL reports 1.5-2.5x higher CPU power consumption for test-case 2

There were no performance improvements in other tests we run on these devices.

Large CPU power usage increase without perf change is visible on:
* SKL i5-6600K (GT2)
* KBL i7-7500U (GT2)
* KBL i7-8809G (GT2)
(And on pre-production CFL-S device we had)

TDP limit caused performance to drop (with increased CPU usage) on:
* KBL i7-7567U (GT3e)
* SKL i7-6770HQ (GT4e)

There was one device where performance increases with the much higher CPU power
usage, but it's only by 1-2% and only in test-case 2:
* SKL i5-6260U (GT3e)

Neither perf nor power usage changed on BXT devices, so I guess this change
concerns only Core devices.

On BDW GT2 the CPU usage increase was clearly smaller than on GEN9 Core devices
(and there was no noticeable performance change).  MediaSDK doesn't support
older devices, so I don't have data from them.

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