Firmware-Based Power Management For Intel Graphics Advances
Written by Michael Larabel in Intel on 17 March 2017 at 05:49 AM EDT. 4 Comments
INTEL --
Intel developers have published their latest version of patches that implement a Single Loop Power Controller (SLPC) as a replacement to host-based power management features.

SLPC can be more efficient than host-based power management features, but as previously covered, it's putting it off into the firmware. Not everyone is happy about Intel's binary-only GuC firmware that is present for Skylake hardware and newer.

Intel's Sagar Arun Kamble provided a refresher over the capabilities of the Single Loop Power Controller:
The SLPC implementation runs in firmware on GuC. This series has been tested with SKL/APL/KBL GuC firmware v9.

The graphics power management features in SLPC in this version are called GTPERF, BALANCER, and DCC.

GTPERF is a combination of DFPS (Dynamic FPS) and Turbo. DFPS adjusts requested graphics frequency to maintain target framerate. Turbo adjusts requested graphics frequency to maintain target GT busyness.

BALANCER adjusts balance between power budgets for IA and GT in power limited scenarios.

DCC (Duty Cycle Control) adjusts requested graphics frequency and stalls guc-scheduler to maintain actual graphics frequency in efficient range.

This patch series activates only GTPERF Turbo in GuC SLPC.
GuC-based SLPC support for the Intel DRM driver is a big addition at 23 patches amounting to nearly two thousand new lines of code. This SLPC support will be available for Skylake, Broxton, and Kabylake hardware. The code is available for review here.

The code is up to its sixth revision so perhaps we'll finally see it land soon, maybe for Linux 4.12. When it does land it will enable this firmware-based power management by default on the supported hardware but can be toggled at boot-time via the i915.enable_slpc argument. When the code lands, I'll run some power tests to see how it compares to the existing power management implementation.

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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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