The report is not so clearly written. Are you saying that Solid mode is slow when the renderer is set to Eevee, but fast if the renderer is set to Cycles? As if Eevee is making it lag even if it isn’t set to Rendered or LookDev mode?

Sorry about that, the lag happens in the viewport regardless of it being in solid mode or wireframe or not, the only time it doesn't happen is if

1. I turn off all display overlays
2. make the window super tiny
3. set it to cycles render in viewport.

All this is just in the startup scene with a cube and nothing else.
And like I said, having the cube selected makes the lag worse (unless overlays are turned off)

Also this is when rotating, panning or zooming or moving the object. doing things in edit mode like extruding, runs smoothly.

Hope that makes it more clear, otherwise I will try to upload a video later today.

A video could be useful.

@Clément Foucault (fclem): any idea why Solid mode could be slower when Eevee is selected vs Cycles? You wouldn’t think it would make a difference. Could it be something like shader compilation in the background or material previews being generated?

Sorry It would seem I might not have expressed it clearly, cycles in solid is still slow, it is when switching to viewport render using cycles it speeds up.

Ah ok. Yes in that case it was not clearly written.

So let me try and understand. You get lag in Solid mode, always? How about Wireframe Mode? And turning off Overlays makes it fast, but in rendered view there’s no lag?

Wireframe is also a problem.
When switching to cycles viewport rendering (like the actual raytracinging rendered in the viewport) it runs smoothly though.

I will try to do a video when I am home.

It feels like it is something with the overlays, as selection highlight is not visible when cycles viewport rendering.

Selection highlights ARE available while in Cycles rendered view, so that’s incorrect.

Yes, sorry you are right disregard that.

Ok, well, in that case it's not so easy to debug this. It's hard to say if this is an actual bug, or if you are simply experiencing poor performance based on the fact that the viewport in 2.8 could be more performant, combined with the fact that you are using relatively high screen resolution on a laptop.

However, on a Macbook Pro here, I do get 'normal' smooth performance, at lease in simple scenes.

Just to clarify, is the default scene with just a cube also laggy?

Okay so I hope it is visible here, the thing is, it is very obvious when you sit with it, but maybe less clear in the video.

Notice that the lag, if ex you focus on the grid is almost gone when in cycles.
And that it feels much smoother when all overlays are turned off.

If it is still not clear, feel free to specify what else you might need.

It feels like for the half to first second I rotate in the view it is fast and smooth, but then immediately slows down.

• sorry did not see your message, I have tested on a macbook with AMD card and it runs super smooth there as well. Notice that mine has nvidia.

I think the problem is might be related to something about blender not triggering my nvidia 750, unless I activate cycles.

I reached this conclusion after working on something with two windows. One rendering in cycles and one just solid shaded. The viewport runs smooth when I start the progressive rendering and stops running smoothly when I pause the render. If this is a bug with blender or my computer I am not smart enough to say.

• I tried to force it to use the 750 by turning off automatic switching in the OS, but didn't help with the lag.

Interesting. Yes, I believe macOS does automatic GPU switching based on load, especially on the older Macbook Pros.

I believe you can use the app gfxCardStatus to monitor this and force it to use a specified GPU: https://gfx.io

Thanks for the link! Just gave it a go, and the problem is the opposite of what I thought, the nvidia card is the one causing the lag, while the integrated one runs smoothly.

And reading up on it, it seems like Apple have just left us Nvidia users hanging with no drivers on Mojave - But at least with gfxCardStatus I can choose to use the intel one.

Just to corroborate, I have a Macbook Pro, same specs as the original poster and I too have the same issue. While the performance is indeed better when forcing the laptop to use the Iris Pro integrated GPU, it unfortunately doesn't change the fact that it's the weaker GPU and that Blender 2.79 didn't have this issue. I've attached a video that clearly shows the difference between the two versions.

This might be a duplicate of T60043. Does using Debug value of 23 fixes the issue?

Performance does seem better when enabling debug value 23, the sporadic lag spikes seem to be gone, performance overall isn't as smooth as 2.79 still, but it definitely helped.

Hang on a moment... So something weird just happened, when the cube is selected the performance is worse than when deselected, weird..
When deselected, performance is like that of 2.79.

Also as that value does seem to improve the performance enough to make the software usable again, is there any way to keep the value enabled and hide the extra stats shown in the viewport? Thanks