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Comment by zarmin | Hacker News Reader

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.

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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.

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.

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.

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.

It's the maxed-out 13in. Intel Iris 1536 MB.

Not a sound.

The 2015 MBP is a work horse but it too had issues with external monitors. I used to connect it to two external 1080p monitors one via HDMI the other with some ancient adapter. When I plugged in the latter my internet would suddenly stop working. This was apparently from a multi year bug where the ports adapter was so close to the wireless card that it interfered with the wireless cards normal operation. Upgrading the adapter fixed the problem (it was one of the old display adapters with physical pins you had to screw in) - took a very long time to debug that issue!

Also, at least macOS provides a consistent resolution for windows, texts, etc. On Windows (after Win 8), many times old applications run with __blurred__ texts and icons while the new shiny Win apps have no such problem. It's actually one of the reasons I don't use Windows anymore, although it's been making good progress.

It's technically consistent, Windows just chooses to rasterize non-DPI-aware applications at the lowest common denominator DPI and scale them up on high-DPI monitors. AFAIK MacOS does the opposite, and rasterizes everything at the highest DPI and then scales down as necessary. The latter looks much better so I'm not totally sure why Windows doesn't do it - perhaps a compatibility hack for apps that expect classic 96dpi.

Newer versions of Win10 actually have an odd variant of this that works more like MacOS where it will sometimes rasterize at a higher DPI and scale down - it looks pretty nice but it's not compatible with all old applications, I only have it enabled for a couple.

But those apps were written for specific resolution and you (probably) cannot make them render themselves with higher resolution. And MacOS unlike Windows simply doesn't support running old apps.

NVIDIA drivers on Windows have an option to scale on the GPU instead of on the monitor, though I'm not certain whether they ever default that on. Presumably it's there as a workaround for people with bad/broken monitors. It'd be interesting to try and measure whether that option raises power draw...

I've never had an NVIDIA driver with it on by default. I've run two different computers with NVIDIA GPU's through a TV and had to manually scale the picture on both of them when I couldn't get the TV's auto scaling to work properly.

I can speak from personal experience that NVIDIA GPUs will use bilinear scaling on Windows to display non-native resolutions on displays that don't have built-in scalers. This isn't a rare situation either. As far as I know, every display with a G-SYNC module inherently does not support display-side scaling. Also worth noting, NVIDIA lets you choose whether to use their scaler or the display's scaler.

I've seen tons of other bugs related to MBP+external monitor over the years, with multiple MBP / OS versions.

My current issue is that I use an ultrawide curved monitor at work, and when I lock the screen and then unlock it, some of my previous window positions are changed on the external monitor. My large-but-not-fullscreened IDE that takes up ~85% of the external monitor is resized and shifted off screen, every time. I have to use the 4-finger swipe up gesture to see all windows, drag the now-visible IDE window into a new desktop panel at the very top, then minimize it from fullscreen, to get back to where I was before I pressed ctrl+cmd+q...

I think the lag is common to all JetBrains IDEs: IDEA, WS, PyCharm, etc. IIRC, it's the JVM not using any acceleration for rendering and there might be another bug whereby using the integrated display and an external 4k panel at the same time causes massive lag. Try closing the lid with your 4k monitor attached and see if things speed up.

In any case, I feel you on the system-wide lag. I basically just avoid using JetBrains products at this point.

I use RubyMine and Webstorm simultaneously on a daily basis with three 1440p monitors (one of which is an ultrawide) and my laptop screen on.

I have absolutely zero lag.

It’s specific to DPI scaling on 4K monitors :(

https://youtrack.jetbrains.com/issue/JBR-526

Yup. Amazing.

wow, a few years ago i was working in java world, and using intellij on a daily basis. any time i used a 4k monitor, i simply could not type anything or scroll through code without insane delay. i googled it and found a ton of people having the same issue. i could only sanely use intellij if i upscaled my resolution to its highest. is this all interconnected?

Same here, but recent versions are much better. If you take a screenshot when running one of the scaled modes on 4k it's actually rendering at a far higher resolution, which then gets scaled down. Almost 6K IIRC, which on a laptop is pretty much insane.

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