A case to use the iGPU if you use two monitors

[Mira Yurizaki]

Since whenever, both AMD and NVIDIA have had a problem when you run multiple monitors off their video cards: they don't downclock to idle. Of course, if you don't care about this (or you a CPU without a iGPU), there's no further need to read on. But if you're interested in saving power and/or lowering your temps because your video card's always running at an elevated power state, read on.

 

In my case, when I have both of my monitors plugged into my GTX 1080, it idles at 1250MHz. Since I don't have EVGA Precision up all the time, the card goes to its "fanless" mode and idles at 65C... which is a little higher than I'd like. So today I thought "why not turn on the iGPU, put my normal use monitor on it, leave the gaming monitor on the graphics card, and see what the power consumption difference is?" For this, I used a Kill-A-Watt to measure power consumption at a fresh reboot and about 5 minutes to settle. Then I used CPU-z stress test and measured the power there. Lastly I put on GTA V's benchmark.

 

With both monitors in the GTX 1080

Idle      72W
CPU       115W
GTAV      250W 

One monitor using the iGPU, the other using the GTX 1080

Idle      35W
CPU       78W
GTAV      250W

So by plugging one of my monitors in the iGPU, I saved 40W if I'm not doing a GPU intensive task. Now I wanted to extend this further and put all my video decoding on the iGPU as well. This means the GTX 1080's only job is to keep a second display up and render games on it. And after fiddling around with MPC-HC and LAV, I got the player to stop using so much dang CPU time and it was still reporting the rendering device was the iGPU. Success!

Spoiler

And what kind of power am I drawing while this is going on? About 75W.

 

How much memory did you sacrifice to run the iGPU?

Since the iGPU has to use system RAM and it's driving a 4K display, I'm letting it use 512MB of RAM. Out of 16GB, if this is too much to spare, then I'm sure 16GB wouldn't be enough either.

 

How are the temps looking?

The CPU never had a problem with temperature. I suspect it has some aggressive thermal throttling but it never really trips it unless I'm really pushing it. The GPU however now settles down to about 45C with the fans off. If I have them on, and it's in the quiet profile, it'll go down to 35C. This is opposed to 65C I mentioned earlier with the fans off and about 48C with them on.

 

Does this affect gaming performance?

I did lose some performance in my GTA V run, but my RAM was finicky when I enabled the iGPU, making me revert it from DDR4-2400 or so back to DDR4-2166. This also meant I lost about 100MHz on the top end of my CPU (because BCLK was bumped up). So I did a 3DMark Fire Strike Extreme run which I had saved before I bumped up my RAM and according to that, I lost about 3%. Not much, but considering how much I save on power when I'm not gaming (which is often), I think that's a fair trade off.

 

In Conclusion...

If you're conscious about keeping your desktop power consumption low and you're running two monitors, have one on the iGPU and the other on the video card. AMD and NVIDIA for many people still have some problem with downclocking their GPUs when plugging in multiple monitors. Plus you can definitely set your computer up so that video players can still take advantage of the iGPU and the iGPU is plenty fast for desktop work anyway. The only thing I'm not sure about is plugging two or more monitors in the iGPU and if Intel's GPUs have the same "won't downclock" issue. Though considering the less power Intel's GPUs still take up, power consumption shouldn't go up that high.

 

Of course, how much does 40W really save? Well if I take my best guess computer usage, it's [(6 hours x 4) + ( 24 hours x 3) ] * 52 weeks = ~200kWh * $0.19134/kWh (this is the summer rate, but I'll leave it up) = $38.27 a year I'll save. But that's if I don't game on the desktop (if I do that, I may as well switch to my laptop)

 

Even if I didn't really care about saving that much money, the fact that the GPU runs a lot cooler and the CPU may be running marginally warmer means my fans aren't working as hard.

[ARikozuM]

I guess my touchscreen will be on the iGPU from now on. Thanks for testing this out for us.

[AshleyAshes]

7 minutes ago, M.Yurizaki said:

Since whenever, both AMD and NVIDIA have had a problem when you run multiple monitors off their video cards: they don't downclock to idle.

Erm, what are you talking about?  I'm running a Radeon R9 390X and it's at it's standard idle clock speed of 300mhz right now, and that's with three monitors attached. o_O

[Mira Yurizaki]

3 minutes ago, AshleyAshes said:

Erm, what are you talking about?  I'm running a Radeon R9 390X and it's at it's standard idle clock speed of 300mhz right now, and that's with three monitors attached. o_O

It's a common issue. People have claimed to have downclocking GTX 1080's on multiple monitors but mine refuses to do so.

 

So I don't know what kind of magic sauce you're pouring on your card.

 

EDIT: If you have three identical monitors that may be it. But a lot of people who multi-monitor buy a new monitor and add it to the pile.

[ARikozuM]

5 minutes ago, M.Yurizaki said:

It's a common issue. People have claimed to have downclocking GTX 1080's on multiple monitors but mine refuses to do so.

 

So I don't know what kind of magic sauce you're pouring on your card.

 

EDIT: If you have three identical monitors that may be it. But a lot of people who multi-monitor buy a new monitor and add it to the pile.

I'm seeing it with the 970. Idle is at 696. I'll check with the 1080 when I put it back in.

[DrMikeNZ]

2 minutes ago, ARikozuM said:

I'm seeing it with the 970. Idle is at 696. I'll check with the 1080 when I put it back in.

I had 3x1080p 60hz monitors connected to a GTX 970 then a GTX 1080, they both idled in the low 100's.

 

Although after I replaced the monitors with 3x 1440p 144hz G-Sync monitors, the 1080 now it idles at 1278 MHz.

[AshleyAshes]

10 minutes ago, M.Yurizaki said:

If you have three identical monitors that may be it. But a lot of people who multi-monitor buy a new monitor and add it to the pile.

Nope.  Two Asus VH236H on DVI plus an Asus PB278Q on HDMI.  (It's nice having a GPU with four TMDS clockgens, I used to have to use DP->DVI adaptors when using GPUs with only two clockgens)

[Mira Yurizaki]

5 minutes ago, DrMikeNZ said:

I had 3x1080p 60hz monitors connected to a GTX 970 then a GTX 1080, they both idled in the low 100's.

 

Although after I replaced the monitors with 3x 1440p 144hz G-Sync monitors, the 1080 now it idles at 1278 MHz.

Yeah, a common point as well seems to be high refresh rate monitors. But I have a 144Hz monitor hooked up to the video card (the other is on the iGPU) and it idles just fine.

 

But I've had this problem since four years ago when I mixed and matched a 1920x1200 monitor with a 2560x1440 monitor, both 60Hz.

 

Either way, I have this problem, a lot of people have this problem, it's found on both camps. I'm just sharing a way to allow the GPU to go to idle if you have a two monitor setup with minimal compromise.

[ARikozuM]

25 minutes ago, M.Yurizaki said:

Yeah, a common point as well seems to be high refresh rate monitors. But I have a 144Hz monitor hooked up to the video card (the other is on the iGPU) and it idles just fine.

 

But I've had this problem since four years ago when I mixed and matched a 1920x1200 monitor with a 2560x1440 monitor, both 60Hz.

 

Either way, I have this problem, a lot of people have this problem, it's found on both camps. I'm just sharing a way to allow the GPU to go to idle if you have a two monitor setup with minimal compromise.

I may be thinking incorrectly but can we assume (or hypothesize rather) that the idles we're seeing are the minimum clocks that our panels require?

[DrMikeNZ]

16 minutes ago, M.Yurizaki said:

Yeah, a common point as well seems to be high refresh rate monitors. But I have a 144Hz monitor hooked up to the video card (the other is on the iGPU) and it idles just fine.

 

But I've had this problem since four years ago when I mixed and matched a 1920x1200 monitor with a 2560x1440 monitor, both 60Hz.

 

Either way, I have this problem, a lot of people have this problem, it's found on both camps. I'm just sharing a way to allow the GPU to go to idle if you have a two monitor setup with minimal compromise.

While I agree that there is a link with high refresh rate monitors, I think there is more going on than just refresh rates.

 

I set all my monitors to 60Hz, the idle clock speed did not decrease.

I disconnected one of the monitors, the idle clock speed reduced to 658 MHz, I disconnected another, it did not decrease further.

I disabled g-sync and reduced resolution to 720p on the single monitor, and it still only idles at 658 MHz, much higher than it did with the old monitors.

[TheLaserCucumber]

I have 2 monitors and my GTX 1070 idled at 139MHz