High Power Consumption of AMD RX6800xt in Idle with Secondary Monitor Connected

[Alex Deucher]

On Mon, Jul 1, 2024 at 3:25 AM Jaroslav Pulchart
<jaroslav.pulchart at gmail.com> wrote:
>
> Dear AMD GPU Kernel Maintainers,
>
> I am writing to report an issue with high power consumption of my AMD
> RX6800xt graphics card when a secondary monitor is connected.
>
> Upon investigation, I observed that my desktop computer generates more
> heat while idling. I determined that the high power consumption issue
> arises when I connect a secondary monitor to my AMD RX6800xt card,
> causing it to consume approximately 40W of power in idle state .
>
> I checked the "GFX Clocks and Power:" in
> /sys/kernel/debug/dri/1/amdgpu_pm_info of my RX6800xt during idle, and
> here are the findings:
>
> With the secondary monitor connected memory frequency is up and
> constantly at 1000MHz:
>         1000 MHz (MCLK)
>         3 MHz (SCLK)
>         1825 MHz (PSTATE_SCLK)
>         1000 MHz (PSTATE_MCLK)
>         856 mV (VDDGFX)
>         45.00 W (average SoC)
>
> Single monitor connected:
>         96 MHz (MCLK)
>         0 MHz (SCLK)
>         1825 MHz (PSTATE_SCLK)
>         1000 MHz (PSTATE_MCLK)
>         6 mV (VDDGFX)
>         8.00 W (average SoC)
>
> The significant difference in power consumption between the two states
> indicates a potential issue in power management that needs to be
> addressed. Your assistance in resolving this matter would be greatly
> appreciated.

It depends on the timing of the monitors.  The memory reclocking can
only occur during blanking periods on the monitors.  If the reclocking
is done outside of the blanking periods, you will see flickering or
artifacts on the display when it happens.  If the blanking periods are
too short the driver can only downclock memory when the displays are
off.  Adding more monitors makes this harder as you have to take into
account the blanking periods on all monitors.  You can try adjusting
the modelines used on each display to increase the blanking periods.

Alex