Finally bought a 5k but something concerns me

[Phil A.]

After almost one year of research in forums and google and thorough study of each model specs I decided to pull the trigger and buy a used 27 5k from eBay, even though that I had reached to a conclusion that it would be better if I waited for the rumored Kaby lake refresh as it would be considerably superior to the current line.

But the price on eBay was very tempting, a 2TB Fusion, m395 total price $1,700 including Apple care until October 2018!! (Fusion was not my first choice though, I'd prefer 512 SSD, maybe in the future if they do a serious refresh I'll sell this one to get pure SSD).
While other similar used macs come only with 1TB fusion or 1TB HDD in that price range and with lower gpu cards.

The machine is in near perfect condition without noticeable flaws or scratches in the screen and the guy was so generous that he even brought it in my house as he was driving by on the same day I purchased it.

Only thing that kinda worries me a bit is that it seems that there is a slight noticeable lag when scrolling safari and other apps, and I don't know if that is perfectly normal or is part of things that I have read that for the 5k you need the top gpu m395x to have the smoothest experience with the graphics.
My uses are web design (WordPress, illustrator, Photoshop, indesign) and heavy browsing, casual video editing in iMovie and FCX. No 3D rendering or gaming at all.

Any thoughts on your own experience with the different gpu models and if the m395 is sufficient enough to push all those pixels on the screen smoothly?

I've got the same spec as you and it's fine for 99.9% of the time. However, occasionally on some websites I do notice a bit of stutter or slow performance: I think it's more down to poor website design than an inherent issue with the iMac though as the vast majority of sites (including very graphically heavy ones) are absolutely fine.

 

[AlexGraphicD]

Oh no...!

I've been lurking the forums while awaiting for the refreshed iMacs for quite some time, and I recall seeing you, AlexGD, also patiently waiting.

And now you've got yourself a machine! I'm starting to feel quite alone.

Yeah, I waited for almost a year to see if a refresh was on the way, but as soon as I saw this awesome deal on eBay I jumped right to it. If this computer covers my needs I will be in no hurry to buy the rumored kaby lake refresh.

*Edit
First I waited for the October 2015 refurbs to come out in the Apple Store and then I started reading online for the rumored 2016 refresh but it never came.

 

[joema2]

That's a 2016 MacBook with discrete GPU that is being demonstrated, not the 2015 model you're referring to.

There are frequent claims the "weak" GPU in the retina iMac 27 is the cause of poor scrolling and other lag in 2D operations. The statement is frequently made the GPU is too weak to "push all those retina pixels around" in those 2D operations.

IF the M395X in a 2015 iMac 27 is too weak to "push all those pixels around", then how can the 2.2Ghz i7 2016 MBP -- without a discrete GPU -- push the pixels of two 5k displays plus its native 2880 x 1800 display -- simultaneously?

One possible answer is all the statements about the GPU pushing around 2D pixels are based on a misunderstanding of what the GPU does and what components are responsible for drawing and moving 2D screen objects.

I don't think we've actually seen a demo of two 5k screens connected to the 2016 15" MBP with integrated graphics, but it is a supported configuration. IF the reasoning is correct about the GPU being responsible for pushing pixels for 2D operations, then I'd expect this configuration to be horrifically slow. The poor little integrated GPU must now handle THREE high resolution retina screens, not just one. It will be interesting to see if anyone actually tests that, how well it works, and what that says about the theory of the GPU being mainly responsible for pushing around pixels for 2D operations.

 

[andy9l]

There are frequent claims the "weak" GPU in the retina iMac 27 is the cause of poor scrolling and other lag in 2D operations. The statement is frequently made the GPU is too weak to "push all those retina pixels around" in those 2D operations.

IF the M395X in a 2015 iMac 27 is too weak to "push all those pixels around", then how can the 2.2Ghz i7 2016 MBP -- without a discrete GPU -- push the pixels of two 5k displays plus its native 2880 x 1800 display -- simultaneously?

One possible answer is all the statements about the GPU pushing around 2D pixels are based on a misunderstanding of what the GPU does and what components are responsible for drawing and moving 2D screen objects.

I don't think we've actually seen a demo of two 5k screens connected to the 2016 15" MBP with integrated graphics, but it is a supported configuration. IF the reasoning is correct about the GPU being responsible for pushing pixels for 2D operations, then I'd expect this configuration to be horrifically slow. The poor little integrated GPU must now handle THREE high resolution retina screens, not just one. It will be interesting to see if anyone actually tests that, how well it works, and what that says about the theory of the GPU being mainly responsible for pushing around pixels for 2D operations.

The 2.2GHz MBP you're talking about is a 2015 model and cannot be used with the 5K monitor - not even one of them. It is categorically not an officially supported configuration.

The 2016 13" models do support one 5K monitor, and they rely on integrated graphics (Iris 540/550).

Macs that support 5K: https://support.apple.com/en-us/HT207448
The 2015 MacBook Pro you keep referring to: http://www.everymac.com/systems/app...-iris-only-mid-2015-retina-display-specs.html

 

[joema2]

The 2.2GHz MBP you're talking about is a 2015 model and cannot be used with the 5K monitor - not even one of them. It is categorically not an officially supported configuration.

The 2016 13" models do support one 5K monitor, and they rely on integrated graphics (Iris 540/550)...

Thanks for that correction. However this does not affect my point in any way whatsoever. If the "weak" M395/M395X GPU in the 2015 iMac7 is responsible for lag in 2D operations like scrolling because it can't push all those 5k pixels around, how does the 2016 13" MBP with only integrated graphics handle two 4k monitors or one external 5k monitor?

Likewise the 2016 15" MBP with Radeon 450 has a Geekbench GPU score of 42827 vs the 85101 of the 2015 iMac 27 with the "weak" M395X GPU. Yet that 2016 15" MBP *can* drive two 5k displays in addition to its native retina display.

Either one of those 2016 MBP machines has a weaker GPU than the 2015 iMac 27 with M395/M395X, which supposedly has lag in 2D operations due to its weak GPU.

If the frequently-stated theory about the GPU being mainly responsible for moving pixels in 2D operations is correct, either of those 2016 MBPs should be extremely laggy when driving one or two 5k screens. I'd be interested if this has ever been tested or observed.

 

[Krevnik]

It was my understanding the GPU is not "running the 5k screen", especially for 2D operations like scrolling. Rather 2D operations are often done by the CPU. There is significant overhead to transfer data to the GPU's memory. This may be worthwhile for a compute-intensive 3D graphics operation, but not necessarily a 2D operation.

Yes and no. This is something that's been changing since the introduction of CoreAnimation, and they work a lot more in unison than they used to in the old days. CoreAnimation layers are backed by the GPU and composited/rasterized by the GPU. On iOS, all UIViews are backed by CoreAnimation layers, and you should be doing the same on Mac (although there are a few more quirks there since AppKit pre-dates CoreAnimation, so it's possible that only your window is backed by a layer, not individual views).

In the case where your views are backed by layers, a layer is backed by a GPU surface/texture. You can draw into the layer, and that happens on the CPU. But if you manipulate the layer by positioning it, animating it, etc, then almost all of that happens on the GPU, since the GPU can just quickly redraw the texture in the new position faster than it would be to redraw it in the new position from scratch. Scrolling is actually an ideal case for this, but since you also draw in the content on-demand, you wind up in this dance of moving the layers for the scroll on the GPU, but also drawing new content into layers on the CPU. Safari in particular leans on the GPU pretty heavily, and I think even bypasses CoreAnimation and uses Metal/OpenGL.

But since you can have older Mac apps where only the window is backed by a GPU surface, then in those cases scrolling is done the old way: redrawing.

The reality is that 2D can benefit quite a bit, if you architect for it. You can offload compositing to it, which is something a GPU does really well and in parallel, but is more expensive on the CPU. And you can change what used to be an expensive CPU blit into something that just happens naturally when the GPU rasterizes (moving part of the screen to a new location). And by expanding it out to cover what the apps do to their views, you get quite a bit of benefit there, since you can wind up sending less data to the GPU per update than if you do all rasterization on the CPU. Your Lightroom example points more to GPGPU compute, which is a more complicated situation since you also need to get the results back to the CPU at some point, and you are sending potentially large datasets over to the GPU to operate on, rather than much smaller updates.

But one thing you are right about is that the GPUs should be able to handle 2D fairly easily. That said, 2D leans much more on fill rate of the graphics card than any other part. And HiDPI screens like the 5K mean textures are 4x the size, so you are pushing 4x the data across to the GPU to composite than you were before. So the needs of 2D GPU work are very different than 3D, and so what makes a good 3D card may not always make for a good 2D card.

Disclaimer: engineering this stuff is something I do for a living.

 

[colinsky]

My late 2015 27" 5K iMac has the M395 GPU and it is running a pair of Dell 27" 2560x1440 monitors besides the 5K screen, and I've never seen any scrolling stutters.

 

[1050792]

My late 2015 27" 5K iMac has the M395 GPU and it is running a pair of Dell 27" 2560x1440 monitors besides the 5K screen, and I've never seen any scrolling stutters.

Then your iMac must have come from the perfect land factory

 

[phpmaven]

How about if one of you shoot a video of what you mean "scrolling stutters" so we can see what you are referring to. I've never seen anything like that on mine either.

 

[1050792]

Here it is.

 

[AlexGraphicD]

My late 2015 27" 5K iMac has the M395 GPU and it is running a pair of Dell 27" 2560x1440 monitors besides the 5K screen, and I've never seen any scrolling stutters.

Well now that puts all my worries away

How about if one of you shoot a video of what you mean "scrolling stutters" so we can see what you are referring to. I've never seen anything like that on mine either.

Here it is.
http://sendvid.com/vlnrdxnd

I understand there probably is no lag at all, I was just expecting a smoother scrolling more like the difference in the eyes when you watch a fast motion video in 30 and 60 fps.

 

[Krevnik]

Here it is.

Yeah, that's definitely one problem with Retina displays, but I'll also point out that the issue is actually not the GPU. "Zooming" the tracks like that trigger redraws which will happen on the CPU. And doing that much work on a single thread will affect framerate.

Buying the higher end GPU won't save you from that. (Although there are some tricks the developers could probably use to improve performance that aren't happening)

 

[varian55zx]

It is well known the GPU affects basic animations in OS X. That is why the M395 model doesn't lag, and the M380 model does. The M380 is a disgusting part that should've never been implemented

M395 is perfectly fine.

 

[MacStu09]

I don't think that is safe to say, mobile GPU improved a lot in recent years so there is no excuse to say it's the GPU fault that can't run the 5k display, but apple's fault for not optimizing their OS for the Hardware graphics-wise.

They definitely have improved a lot, but even with that being said, the m395 is still far behind mid-range cards of three years ago in real performance. There's no reason they should've used such a weak card in such an expensive computer. But you're right, I think in this specific case, it's more an issue of the OS.

 

[joema2]

Reviewing the responses (and thanks to Krevnik for the detailed technical info): AlexGraphicD was concerned the iMac 27 M395 GPU was the cause of a slight lag when scrolling in Safari. This resulted in responses that some lag is expected in such 2D scrolling operations because the iMac uses a weak mobile GPU. This is a common response, as the GPU in 5k iMac is often described as too weak to "push all those pixels around". Is there anything we can learn from this?

The M395 GPU in the iMac 27 benchmarks faster than Radeon 450 in the 2016 15" MBP -- which can drive *two* 5k displays plus its native retina display. If the theory about a weak mobile GPU being the cause of laggy scrolling is correct, we should expect extremely sluggish scrolling on the Radeon 450-equipped MBP with two 5k monitors or four 4k monitors.

In the 2 x 5k case, the Radeon 450 on the 2016 15" MBP is driving 34.6 megapixels -- 2.35 times the pixels of a 27" retina iMac. In the 4 x 4k case it is driving 42.9 megapixels -- 2.9 times the pixels of a retina iMac 27. I haven't see actual tests of this but I doubt it will be unusably slow.

If the scrolling performance in those cases is OK, it will strongly imply the theory about the "weak" GPU being responsible for laggy scrolling is not correct.

As Krevnik explained, 3D performance is very different from 2D performance. While faster 3D performance would be welcome in the iMac 27 (and likely expected in the next update), that does not mean any 2D lag is the fault of the M395 GPU.

As Krevnik also explained, many operations you perceive as laggy are not GPU-bound, but require CPU operations to process. Just because it happens on the screen doesn't mean it is always handled by the GPU.

Ironically it now appears there was no lag whatsoever in the behavior AlexGraphicD observed.

 

[vddobrev]

I get severe lag in iTunes on my iMac with specs from my signature. The lag is mostly noticed when in Albums grid view, or in Recently Added. When I click on an album cover to reveal the song list, it lags a lot, i.e. it will take some time to show the list of songs, and the animation is not at all rendered, it just show the list. The same is noticed when an album is expanded with list of songs, and you click on another album. In comparison, my Mac mini and MacBook Pro are fluid with the same operations in iTunes.

 

[ryannel2003]

It is well known the GPU affects basic animations in OS X. That is why the M395 model doesn't lag, and the M380 model does. The M380 is a disgusting part that should've never been implemented

M395 is perfectly fine.

I see you saying this quite a bit and don't see any real facts backing up your comments. I have the M380 model and the only lag I have ever noticed was in iTunes under recently added (which the poster above me also has an issue with and he has the M395) or when using Mission Control with lots of windows open. Otherwise the computer runs perfectly fine.

 

[varian55zx]

I see you saying this quite a bit and don't see any real facts backing up your comments. I have the M380 model and the only lag I have ever noticed was in iTunes under recently added (which the poster above me also has an issue with and he has the M395) or when using Mission Control with lots of windows open. Otherwise the computer runs perfectly fine.

I have great attention to detail, so I am able to notice.

Take my word for it, I've owned both and the differences are obvious.

 

[ryannel2003]

Maybe so. I just don't notice it and since I don't tax the computer frequently it's not something that would bother me if it did happen.

 

[vddobrev]

I have great attention to detail, so I am able to notice.

Take my word for it, I've owned both and the differences are obvious.

Can you try in iTunes what I said above? Go in Albums view and click on an album.

 

[varian55zx]

Maybe so. I just don't notice it and since I don't tax the computer frequently it's not something that would bother me if it did happen.

As I have mentioned I have great attention to detail and a wonderful keen eye, I now know most people here do not. I am not extending that judgment to you, I don't know if you do or not.

I noticed lag in nearly every operation on the M380, from opening apps (the bouncing animation), to opening notification center, to using the stacks feature in the dock.

Those things lagged much more with the M380 vs the M395. I am not making this up. These are objective observations that can be observed.

I was also on the 2tb fusion drive on the M380 vs the 512 SSD on my M395 machine, but that shouldn't affect lag.

If you don't have one with an M395, the only way you could do it if you don't have one you can try is to compare it with the demo at the Apple Store. At least in California, pretty much every Apple Store has an M395/2 tb model out. They do not lag.

Can you try in iTunes what I said above? Go in Albums view and click on an album.

I just gave what you mentioned a try on M395 machine, 3.3 i5, 512gb SSD.

There is next to no lag, and I'm probably the biggest critic of lag here, I'm the only one who criticizes the M380 (yes it is worse).

The lag in album / recently added view when clicking the album icon to view the song list is minimal to nonexistent on my machine, and a non-issue.

Your lag is probably a result of your fusion setup, a great deal of that music data would lie on the spinner, which of course is very slow. I doubt it is a result of the GPU in this instance.

My music data is on an (unfused) external HDD, but since my system is running off the (incredibly fast) pure flash, everything I do will be considerably faster than any other type of setup.

 

[1050792]

I recently noticed that while using Chrome there is much more noticeable UI lag than while using Safari. Can anyone confirm this theory?

 

[varian55zx]

I wanted to post a little update in this thread.

I just had the chance to try the m395 / 2tb fusion iMac.

It lags like hell in iTunes when you're in album view, and click the album to view the songs in the album.

Alternatively, my iMac is the 512 SSD iMac and there is next to no lag at all. Additionally, my music library is even kept on a plain external HDD, and my music library is much larger than the one on the iMac I tested.

The reason for this is not the graphics processor but the fusion drive. Just as I predicted all along.

Fusion results in lag throughout various operations, this being one of them. Still think I'm making it up?

 

[vddobrev]

I wanted to post a little update in this thread.

I just had the chance to try the m395 / 2tb fusion iMac.

It lags like hell in iTunes when you're in album view, and click the album to view the songs in the album.

Alternatively, my iMac is the 512 SSD iMac and there is next to no lag at all. Additionally, my music library is even kept on a plain external HDD, and my music library is much larger than the one on the iMac I tested.

The reason for this is not the graphics processor but the fusion drive. Just as I predicted all along.

Fusion results in lag throughout various operations, this being one of them. Still think I'm making it up?

Thanks for confirming, this is exactly my iMac, and it "lags like hell in iTunes", as I previously posted. Now, how safe is it to un-fusion the fusion drive and use only the SSD portion for OS and iTunes Library?

 

[1050792]

I wanted to post a little update in this thread.

I just had the chance to try the m395 / 2tb fusion iMac.

It lags like hell in iTunes when you're in album view, and click the album to view the songs in the album.

Alternatively, my iMac is the 512 SSD iMac and there is next to no lag at all. Additionally, my music library is even kept on a plain external HDD, and my music library is much larger than the one on the iMac I tested.

The reason for this is not the graphics processor but the fusion drive. Just as I predicted all along.

Fusion results in lag throughout various operations, this being one of them. Still think I'm making it up?

That is possibly not true. I'm using the 395x with the SSD and my iTunes lags like there is no tomorrow. Are you using the latest version of Sierra in your iMac?