7 ms·

This appears to be a software bug in macOS or AMD's drivers. Plugging in an external monitor at certain resolutions (1440p@60Hz in my case) will cause the AMD G

by gnudad 7y ago

This appears to be a software bug in macOS or AMD's drivers. Plugging in an external monitor at certain resolutions (1440p@60Hz in my case) will cause the AMD GPU to draw 18-20W constantly, no matter what it's doing. This causes the total system draw to increase from ~10W to ~30W. All that heat has to go somewhere. If I change the resolution of my external monitor to 1080p the AMD GPU drops to ~4W and the fans are quiet again. A lot more information available in this long MacRumors thread: https://forums.macrumors.com/threads/16-is-hot-noisy-with-an-external-monitor.2211747/page-22 https://forums.macrumors.com/threads/16-is-hot-noisy-with-an...

splatcollision 7y ago
Can you share how you're measuring GPU power draw? I have just migrated to a 16" MBP with the AMD chip, and also use an external display some of the time. Have noticed the fan noise and heat but it hasn't been a problem yet.
- masklinn 7y ago
  I’d guess they measure total draw and compare against their baseline eg when they say the GPU draws 20W it’s 20W more than whatever the draw is when only using the internal display.
- gnudad 7y ago
  I use iStat Menus and look at the "Radeon High Side" sensor for GPU power draw under the Sensors menu icon.
  - splatcollision 7y ago
    Cool, thanks for that
nileshk 7y ago
I have medium-to-high fan noise/RPM consistently when connected to an Apple TB display (2560x1440@60Hz), but it's much quieter when connected to a 2560x1600@60Hz monitor. So if it is very specific resolutions, but not necessarily higher resolutions in general, that matches my experience.
333c 7y ago
That's interesting. I was watching a movie on my 1440p@60hz monitor last night on my 16" MBP in clamshell mode and the fans were on the whole time. That sounds like a connection.
- deleted 7y ago
  [deleted]
tpmx 7y ago
So I first thought that using gfxCardStatus to force the use of integrated graphics could help. However: > gfxCardStatus v2.3 and above actively prevents you from switching to Integrated Only mode when any apps are in the Dependencies list (or if you have an external display plugged in). This is because if you were to do this, your discrete GPU would actually stay powered on, even though you've switched to the integrated GPU. https://gfx.io/switching.html#integrated-only-mode-limitations https://gfx.io/switching.html#integrated-only-mode-limitatio...
- bluedino 7y ago
  Because of the way the ThunderBolt ports are wired, you cannot use external graphics without activating the discrete GPU. It's been like this in MacBook Pros for a long time.
  - dman 7y ago
    Thats messed up
kevingadd 7y ago
fwiw NVIDIA GPUs have had a similar behavior under normal conditions on Windows forever. After following up with tech support about it, the explanation provided can basically be summarized as 'the higher the resolution + refresh rate of your attached monitors, the more demand placed on the memory controller and scan-out, which means a higher minimum GPU and/or memory clock to drive it'. My current RTX 20xx card can drive two 4k monitors at low clocks, but the 9xx series really struggled and the 10 series still needed to clock up some. I suspect something similar is probably happening here with the AMD GPU if you're running the laptop's integrated retina display along with a 1440p60 external display, it's probably forced to clock up to drive that many pixels. I'm not really sure how AMD could get around basic hardware limitations here unless they have a really clever way of driving displays at a low memory clock.
- sudhirj 7y ago
  It seems more related to 1440p specifically. People reporting no issues with higher resolutions.
  - tpmx 7y ago
    I have a 2160p external monitor attached to my MBP 16" via Thunderbolt/Displayport 1.2 at 60 Hz. I tried out the five different "Looks like" scalings the Display Preferences allow for and then eyeballed the "Radeon High Side" wattage readouts via iStat Menus: 1280x720: 18W 1920x1080: 6W 2560x1440: 6W 3200x1800: 6W 3840x2160: 6W So it looks like it might (also?) be related to the display resolution scaling.
    - kevingadd 7y ago
      It would make sense if situations where the native panel resolution doesn't match the framebuffer resolution are causing the driver stack to have to maintain two framebuffers (native and non-native) to do the upscale and then feed it to the monitor. GeForce drivers on windows specifically have a setting to control whether this happens or not (let the monitor scale it, have the GPU scale it). The upscale would not only use more VRAM in that case (and as a result more memory bandwidth) but it'd need a bit more GPU compute as well to perform the scaling. On my low-spec laptop from a while back, running Rising Thunder set to 720p was faster than native, but it was even faster to first set my desktop resolution to 720p because the overhead of the game engine scaling its 720p framebuffer up to native 4k was measurable. Setting the desktop resolution down also improved battery life.
zarmin 7y ago
This is a bug on Macbooks in general, as I understand it. I have a 2019 MBP with a 4k monitor, and if I change the resolution to anything except the default, there is massive system-wide lag. God forbid I use PyCharm on 4k scaled resolution – a full second between typing and seeing the text.
- nottorp 7y ago
  That seems unrelated; I think Mac OS is the only place where non native resolutions use GPU-accelerated scaling. The other operating systems just set whatever resolution you asked for and let the monitor handle it. This seems to be excessive GPU use when simply connecting an external monitor at its native res.
  - muyuu 7y ago
    I use my 2015 MBP with an external 4K monitor every day and it works like a charm. No delay, no fans going off, etc.
    - ecliptik 7y ago
      Does it have two GPUs it switches between? One high perf and one integrated? When I had a MBP 2015 I rarely had the fan come because it only had and and used an integrated GPU. With a 2018 MBP the fan frequently kicks on because it switches to the Radeon high perf GPU when doing things like connecting to an external monitor.
      - nigma 7y ago
        The MBP 2015 with discrete GPU is hardwired to output video signal through AMD M370X. It can get quite noisy when just connected to an external display.
      - muyuu 7y ago
        It's the maxed-out 13in. Intel Iris 1536 MB. Not a sound.
    - 7y ago
mortenjorck 7y ago
I’m curious if this is affected by the resolution on the laptop display. I believe the 16” and more recent 15” all default to a slightly scaled resolution, versus the pre-Touch Bar 15” which defaults to the panel’s native 2x resolution.
- spiralganglion 7y ago
  I'm using the MBP in clamshell driving a 2560x1440@60 Apple Cinema Display at native res, and seeing the GPU drawing 20W constantly (via iStat Menus). The laptop's internal display is set to native 2x. The fans sit just fine at the minimum speed under this setup, nice and quiet... until I start to do anything even remotely demanding, like, oh, open Ableton Live. Used to be I could run dozens of tracks and plugins with no fan noise. Now I can't even have a blank project open without the fans spinning up to audible levels. So much for recording vocals!
hrrsn 7y ago
I’ve noticed this too using an HP Thunderbolt Dock G2 with a 16” and 2x 4K60 monitors. I just assumed it was because it’s summer here and the laptop tends to sit in the sun a bit, but it’d be nice if it got fixed.
mvkel 7y ago
This would explain why when an external monitor is plugged in, my battery drains despite being on a charger. When it reaches 5% battery, the CPU load goes to 800%. The fix? Unplug the external monitor.
- favadi 7y ago
  That sounds like your laptop has a defected battery.

by gnudad 7y ago

splatcollision 7y ago

Can you share how you're measuring GPU power draw? I have just migrated to a 16" MBP with the AMD chip, and also use an external display some of the time. Have noticed the fan noise and heat but it hasn't been a problem yet.

masklinn 7y ago
I’d guess they measure total draw and compare against their baseline eg when they say the GPU draws 20W it’s 20W more than whatever the draw is when only using the internal display.
gnudad 7y ago
I use iStat Menus and look at the "Radeon High Side" sensor for GPU power draw under the Sensors menu icon.
- splatcollision 7y ago
  Cool, thanks for that

nileshk 7y ago

I have medium-to-high fan noise/RPM consistently when connected to an Apple TB display (2560x1440@60Hz), but it's much quieter when connected to a 2560x1600@60Hz monitor. So if it is very specific resolutions, but not necessarily higher resolutions in general, that matches my experience.

333c 7y ago

That's interesting. I was watching a movie on my 1440p@60hz monitor last night on my 16" MBP in clamshell mode and the fans were on the whole time. That sounds like a connection.

deleted 7y ago
[deleted]

tpmx 7y ago

So I first thought that using gfxCardStatus to force the use of integrated graphics could help. However: > gfxCardStatus v2.3 and above actively prevents you from switching to Integrated Only mode when any apps are in the Dependencies list (or if you have an external display plugged in). This is because if you were to do this, your discrete GPU would actually stay powered on, even though you've switched to the integrated GPU. https://gfx.io/switching.html#integrated-only-mode-limitations https://gfx.io/switching.html#integrated-only-mode-limitatio...

bluedino 7y ago
Because of the way the ThunderBolt ports are wired, you cannot use external graphics without activating the discrete GPU. It's been like this in MacBook Pros for a long time.
- dman 7y ago
  Thats messed up

kevingadd 7y ago

fwiw NVIDIA GPUs have had a similar behavior under normal conditions on Windows forever. After following up with tech support about it, the explanation provided can basically be summarized as 'the higher the resolution + refresh rate of your attached monitors, the more demand placed on the memory controller and scan-out, which means a higher minimum GPU and/or memory clock to drive it'. My current RTX 20xx card can drive two 4k monitors at low clocks, but the 9xx series really struggled and the 10 series still needed to clock up some. I suspect something similar is probably happening here with the AMD GPU if you're running the laptop's integrated retina display along with a 1440p60 external display, it's probably forced to clock up to drive that many pixels. I'm not really sure how AMD could get around basic hardware limitations here unless they have a really clever way of driving displays at a low memory clock.

sudhirj 7y ago
It seems more related to 1440p specifically. People reporting no issues with higher resolutions.
- tpmx 7y ago
  I have a 2160p external monitor attached to my MBP 16" via Thunderbolt/Displayport 1.2 at 60 Hz. I tried out the five different "Looks like" scalings the Display Preferences allow for and then eyeballed the "Radeon High Side" wattage readouts via iStat Menus: 1280x720: 18W 1920x1080: 6W 2560x1440: 6W 3200x1800: 6W 3840x2160: 6W So it looks like it might (also?) be related to the display resolution scaling.
  - kevingadd 7y ago
    It would make sense if situations where the native panel resolution doesn't match the framebuffer resolution are causing the driver stack to have to maintain two framebuffers (native and non-native) to do the upscale and then feed it to the monitor. GeForce drivers on windows specifically have a setting to control whether this happens or not (let the monitor scale it, have the GPU scale it). The upscale would not only use more VRAM in that case (and as a result more memory bandwidth) but it'd need a bit more GPU compute as well to perform the scaling. On my low-spec laptop from a while back, running Rising Thunder set to 720p was faster than native, but it was even faster to first set my desktop resolution to 720p because the overhead of the game engine scaling its 720p framebuffer up to native 4k was measurable. Setting the desktop resolution down also improved battery life.

zarmin 7y ago

This is a bug on Macbooks in general, as I understand it. I have a 2019 MBP with a 4k monitor, and if I change the resolution to anything except the default, there is massive system-wide lag. God forbid I use PyCharm on 4k scaled resolution – a full second between typing and seeing the text.

nottorp 7y ago
That seems unrelated; I think Mac OS is the only place where non native resolutions use GPU-accelerated scaling. The other operating systems just set whatever resolution you asked for and let the monitor handle it. This seems to be excessive GPU use when simply connecting an external monitor at its native res.
- muyuu 7y ago
  I use my 2015 MBP with an external 4K monitor every day and it works like a charm. No delay, no fans going off, etc.
  - ecliptik 7y ago
    Does it have two GPUs it switches between? One high perf and one integrated? When I had a MBP 2015 I rarely had the fan come because it only had and and used an integrated GPU. With a 2018 MBP the fan frequently kicks on because it switches to the Radeon high perf GPU when doing things like connecting to an external monitor.
    - nigma 7y ago
      The MBP 2015 with discrete GPU is hardwired to output video signal through AMD M370X. It can get quite noisy when just connected to an external display.
    - muyuu 7y ago
      It's the maxed-out 13in. Intel Iris 1536 MB. Not a sound.
  - 7y ago

mortenjorck 7y ago

I’m curious if this is affected by the resolution on the laptop display. I believe the 16” and more recent 15” all default to a slightly scaled resolution, versus the pre-Touch Bar 15” which defaults to the panel’s native 2x resolution.

spiralganglion 7y ago
I'm using the MBP in clamshell driving a 2560x1440@60 Apple Cinema Display at native res, and seeing the GPU drawing 20W constantly (via iStat Menus). The laptop's internal display is set to native 2x. The fans sit just fine at the minimum speed under this setup, nice and quiet... until I start to do anything even remotely demanding, like, oh, open Ableton Live. Used to be I could run dozens of tracks and plugins with no fan noise. Now I can't even have a blank project open without the fans spinning up to audible levels. So much for recording vocals!

hrrsn 7y ago

I’ve noticed this too using an HP Thunderbolt Dock G2 with a 16” and 2x 4K60 monitors. I just assumed it was because it’s summer here and the laptop tends to sit in the sun a bit, but it’d be nice if it got fixed.

mvkel 7y ago

This would explain why when an external monitor is plugged in, my battery drains despite being on a charger. When it reaches 5% battery, the CPU load goes to 800%. The fix? Unplug the external monitor.

favadi 7y ago
That sounds like your laptop has a defected battery.