Linux 7.3 adds new power-saving mode for Intel Xe3 graphics
Intel is preparing a new display power-saving function for Xe3 integrated graphics in Linux 7.3. The change allows Panther Lake processors and newer platforms to reduce their internal fabric frequency when the display requires little memory bandwidth.
An integrated display engine reads completed images from system memory before sending them to the laptop panel or an external monitor. The processor must keep its memory fabric operating fast enough to handle this traffic. However, the lowest standard frequency level can still provide more bandwidth than some display configurations require.
New 20 GB/s bandwidth point
Intel’s patch adds another QGV operating point with peak and reduced bandwidth values set to 20 GB/s. The driver can select this level when the calculated display data rate falls below the 20 GB/s threshold.
“On Xe3+, the SoC can lower the fabric frequency when the display needs less bandwidth than the minimum GV point. This threshold is defined as 20 GB/s. The driver can choose to request this threshold when the required data rate falls below it.
Add an extra QGV entry, with both peak bw and derated bw set to 20 GB/s, to the bandwidth info when all of the following hold:
1. The platform is Xe3+.
2. There is at least one existing QGV point.
3. The number of QGV points is below 8 (the maximum).Once a plane group is found, the driver iterates over all QGV points in that group to find the best match for the required data rate. If the required data rate is below 20 GB/s, it selects the peak bw from this new QGV point (20 GB/s).”
The new point is added only on Xe3 or newer display hardware. The system must support QGV frequency management and have room for another point within the limit of eight entries. Intel says the SoC can then lower the fabric frequency below the previous minimum level.
No graphics performance increase
This does not limit system memory bandwidth or the performance available to the Xe3 GPU. The 20 GB/s value is used only when selecting a power state for display traffic. More demanding configurations, including high-resolution or high-refresh-rate monitors, can continue using faster fabric levels.
The expected result is lower SoC power use during less demanding display workloads, such as desktop use or video playback. Intel has not provided power consumption or battery runtime figures. The same Linux 7.3 driver update also enables UHBR link rates for DisplayPort connections tunneled through Thunderbolt.
Source: Phoronix
