Huge CPU lag with external monitors


Lukest

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Hi there,

I have searched 4 pages (four!!) of Google trying to find a solution to my problem but none seem to fix it exactly.

I am getting unbelievable lag when I am using more than one monitor. i.e. when I connect two external monitors and close my lid, or connect one monitor and use my Macbook display.
I have a feeling this is a GPU issue, but there are reports of people on the same GPU with no issues.

Here's the situation:
MacBook Pro (15" Retina, Mid 2012)
Processor: 2.6 GHz Intel Core i7 Quad core
Memory: 8GB 1600Mhz DDR3
Graphics: Intel HD Graphics 4000 1536MB & NVIDIA GeForce GT 650M 1GB
Attempting to connect: 2x Dell S2418H monitors (1 via HDMI and 1 via DisplayPort to HDMI) - both @ 1920 x 1080

Actual issue: kernal_task spikes to 1000% CPU usage (I've seen it at 2.5k%) and makes computer unusable.

Screen Shot 2017-12-04 at 8.53.53 pm.png


I'd have thought that having two graphics cards would help, but I have heard whispers on the street that the HDMI and DisplayPort ports are not connected to one of them so it cannot utilise both for external monitors. I hope this is not true. I have attempted to use dynamic switching to no avail.

Can anyone help me troubleshoot? Your help is much appreciated.

Cheers,

Luke
 
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honestone

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Not sure if it makes a difference, but what exact Mac OS are you using? Did this issue start after you "upgraded" to the new OS?
 

Lukest

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Not sure if it makes a difference, but what exact Mac OS are you using? Did this issue start after you "upgraded" to the new OS?
Hi Honestone,

Thanks for the reply.
This has occurred on Yosemite, El Capitan, and also High Sierra now. I never had much of a problem with the lag because I didn't use external monitors as much as I do now.

I have a Macbook Pro (13") for work that has lower specs but is able to handle dual monitors (on a single graphics card).
 

honestone

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Did you ever use Sierra, and if so, did the issue occur with that OS also?
 

Lukest

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Did you ever use Sierra, and if so, did the issue occur with that OS also?
I don't believe I used Sierra, but I only recently started using monitors more frequently since I was on High Sierra. However I have experienced this issue previously whenever I would use an external monitor (which was only every now and then).

I have a gut feeling it is a hardware issue, since my fans spin up to max and the lag is coming from kernal_task using so much of the CPU that it has no power left.

I am not 100% sure what kernal_task actually is but it is definitely the culprit.
 
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Lukest

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Hello and welcome.

It may be related to the dual graphics processors in that model MBP that you mentioned:
MacBook Pro: How to determine which graphics processor is in use

Try setting it to use the discrete NVIDIA graphics only:
Set graphics performance on MacBook Pro

-Does it happen more with any particular monitor(s)?
-What brand is the Mini DisplayPort to HDMI adapter?

C

I have tried forcing the gfx card manually with an app called gfxCardStatus.

Also my 'About This Mac' shows that I am using the Nvidia for both of them.
Screen Shot 2017-12-06 at 9.14.21 pm.png


The adapter I am using is a Belkin brand, which is sold at Apple shops (so I hope it is not the cause!).

Here's my system report for the gfx card:
Screen Shot 2017-12-06 at 9.16.53 pm.png


By the way, it gets much worse the more peripherals I use. When I connect my speakers via USB, then connect a USB mouse, and a bluetooth keyboard... it gets a bit worse, but the monitors do the brunt of the work in making my computer crap itself.

Hope this helps, and thanks you all for your replies. I hope we can solve this.

Cheers,

Luke
 

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