Linux 4.20 Allows Overclockers To Increase The Radeon TDP Power Limit

[phoronix]

Phoronix: Linux 4.20 Allows Overclockers To Increase The Radeon TDP Power Limit

The AMDGPU Linux kernel driver for a while has now offered command-line-driven OverDrive overclocking for recent generations of Radeon GPUs. This has allowed manipulating the core and memory clock speeds as well as tweaking the voltage but has not supported increasing the TDP limit of the graphics card: that's in place with Linux 4.20..

http://www.phoronix.com/scan.php?page=news_item&px=Linux-4.20-Increase-AMD-GPU-TDP

[Solid State Brain]

Partially unrelated, but I'm on 4.20.0 and when I enable the boot flag to allow overclocking on my RX480 I get extreme screen screen flickering when I enable a second display. This is likely due to memory clock not getting adjusted as it should to higher values, compared to when no boot flag is used. Has anybody else observed this issue? It's been like this for several kernel versions and makes Radeon GPU overclocking on Linux unusable in my case.

[Zucca]

Do people really benefit overclocking their GPUs?
I could potentially test this... I have water cooled R9 Nano. I could get it ot Fury X perforrmance levels this way maybe. But is it worth of it?

[cRaZy-bisCuiT]

Do people really benefit overclocking their GPUs?
I could potentially test this... I have water cooled R9 Nano. I could get it ot Fury X perforrmance levels this way maybe. But is it worth of it?

Well, having 50 instead of 40 FPS e.g. could be worth it because it feels smooth at times where it did not before. I don't know if you have such edge cases. Having 100 or 110 FPS might not make any difference.

[BS86]

Do people really benefit overclocking their GPUs?
I could potentially test this... I have water cooled R9 Nano. I could get it ot Fury X perforrmance levels this way maybe. But is it worth of it?

Highly depends on the chip. Vega for example does not benefit from overclocking (it mainly increases energy consumption with close to no FPS gains), while Polaris does benefit from overclocking. On the other hand, Vega does not loose much performance when "underclocking", but uses less energy.

From what I remember, the Fiji Chips used in Fury/Nano cards also did not benefit much from overclocking.
Edit: However, the Nano and Fury X use the same Fiji XT chip, so you should basically get your Nano to Fury X performance levels as long as your cooling solution can deal with the increased heat.

[dungeon]

Do people really benefit overclocking their GPUs?

Of course, when you don't have artifacts you can overclock GPU do get some.

After recent nouveau user comment on google chrome i really started to believe that there people who prefer to have artifacts even on Desktop

[Girolamo_Cavazzoni]

Partially unrelated, but I'm on 4.20.0 and when I enable the boot flag to allow overclocking on my RX480 I get extreme screen screen flickering when I enable a second display. This is likely due to memory clock not getting adjusted as it should to higher values, compared to when no boot flag is used. Has anybody else observed this issue? It's been like this for several kernel versions and makes Radeon GPU overclocking on Linux unusable in my case.

I have observed the same issue. I am back to one monitor now (mainly because of another reason, though [different subpixel matrix]) and everything works as expected with overclocking.

Do people really benefit overclocking their GPUs?
I could potentially test this... I have water cooled R9 Nano. I could get it ot Fury X perforrmance levels this way maybe. But is it worth of it?

Yes, people do. I have an RX 470 with 8 GiB VRAM which clocks rather low - especially the VRAM. Since it is specified to clock way higher (2000 MHz instead of 1650 MHz) than preconfigured not to overclock is wasting potential. Polaris needs memory bandwith as high as possible.

[Mathias]

if (limit > max_power_limit)
return -EINVAL;

What Happens if one simply removes that check? Can you overclock above the bios level? I assume no, but maybe someone knows for sure.

[Noee]

Partially unrelated, but I'm on 4.20.0 and when I enable the boot flag to allow overclocking on my RX480 I get extreme screen screen flickering when I enable a second display. This is likely due to memory clock not getting adjusted as it should to higher values, compared to when no boot flag is used. Has anybody else observed this issue? It's been like this for several kernel versions and makes Radeon GPU overclocking on Linux unusable in my case.

Same issue here on RX560, but if I choose High or Low, seems fine. Auto is where the flickering comes back (with multi-mon). Happens with 5.0 kernels so far as well.

[jrdoane]

Highly depends on the chip. Vega for example does not benefit from overclocking (it mainly increases energy consumption with close to no FPS gains), while Polaris does benefit from overclocking. On the other hand, Vega does not loose much performance when "underclocking", but uses less energy.

From what I remember, the Fiji Chips used in Fury/Nano cards also did not benefit much from overclocking.
Edit: However, the Nano and Fury X use the same Fiji XT chip, so you should basically get your Nano to Fury X performance levels as long as your cooling solution can deal with the increased heat.

So, I have a Vega 64 and altering the power cap does impact performance depending on the use case if you're already pushing the GPU to the power cap because when this occurs, the GPU automatically throttles clocks and voltages down to a power state to keep power utilization at or below the cap. In fact it maintains higher clocks for longer because it's not being throttled due to hitting the power cap when you raise the cap, so even without an overclock, you're likely to see higher maximum frame rates. With that said though, once my Vega 64 gets to 85*C, it starts throttling due to thermals instead of hitting the power cap when I raise it without altering the fan speed.

The reason under-volting works to improve performance on these chips is because lower voltage means less power draw, so you're not bouncing off the power limit as often which means the GPU is maintaining higher power states for longer without dropping to a lower power state to keep power draw at or below the cap. The end result is a higher average clock speed, which is what raising the power cap essentially does (if it doesn't thermal throttle.)

Also consider this for overclocking, if clocking it higher increases power draw and you're already hitting the power cap, you very well might be forcing the GPU into lower power states than at stock if that causes power draw to increase at particular power states (which it will, particularly at the highest power states where the voltage is highest.)

tl;dr: You won't benefit from any overclock if your already bouncing off the power cap because it'll never actually run the GPU full tilt.