Weird regular graphic issue - throttling?

[imacken]

When playing games, I experience a regular graphic issue on my late 2015 27" iMac with M395X, and that is an effect that is like walking through treacle. It's like the graphics jerk forward, so normal for a second then kind of stuck in treacle for a second, then repeat the pattern ad nauseam. Only a restart makes this go away.
This also occurs at times in Bootcamp, and is independent of what game I am playing, so I can only assume this is hardware related.
It occurred to me that it might be throttling of the GPU as looking at iStat, the temps are constantly over 100 degrees when playing games.
Any ideas on this?

 

[AtomicGrog]

What games? are they the GPU intensive ones? Are you attempting to run at full graphics content (and in Retina resolution)?

A few reaching thoughts:

1. OSX : these may be poor OSX ports (running wine etc. to emulate)

2. Maybe bootcamp/windows doesnt have optimised drivers.

3. That card was top of range for the iMac at time, not sure if you got the 4GB memory. 2 GB might be the cause if you are pushing boundaries. That said it's not exactly 'top tier' for gaming.

4. Alternatives might be your internet connection, are you playing online games? Eve Online use to freak out for me in massive battles.

5 Only a restart makes it go away.. even in bootcamp/windows? very odd, Really need to know more about the games you are running.

 

[imacken]

Thanks for that.
1) games are not poor macOS ports. I’m talking about Feral games like Hitman, F1 2017, DiRT Rally, etc.
2) drivers are not the issue. I use the latest AMD Crimson as made available from bootcampdrivers.com.
3) it’s the 4Gb version, and is perfectly good for playing most games at 1440p on high settings, giving usually between 40 and 60 FPS.
4) I don’t play online games, but my internet connection is very good and is a steady 40mbps.
5) I know that sounds weird, but I assume it must be to do with letting everything cool down. I really don’t know.
What I do know, though, is that the GPU reaches a pretty constant 105-109 degrees through these game sessions, and that is why I wondered if this was throttling I am experiencing.

 

[h9826790]

Thanks for that.
1) games are not poor macOS ports. I’m talking about Feral games like Hitman, F1 2017, DiRT Rally, etc.
2) drivers are not the issue. I use the latest AMD Crimson as made available from bootcampdrivers.com.
3) it’s the 4Gb version, and is perfectly good for playing most games at 1440p on high settings, giving usually between 40 and 60 FPS.
4) I don’t play online games, but my internet connection is very good and is a steady 40mbps.
5) I know that sounds weird, but I assume it must be to do with letting everything cool down. I really don’t know.
What I do know, though, is that the GPU reaches a pretty constant 105-109 degrees through these game sessions, and that is why I wondered if this was throttling I am experiencing.

If it's throttling, restart should not be required to "fix" the issue. Technically, once you leave the game, the GPU will cool down straight away and back to normal state.

Since you said the same problem exist in both MacOS and Windows, therefore, it's highly likely hardware related.

And since you mentioned the GPU constantly run at 105-109C. I suspect it's a premature hardware failure.

If I were you, I will take the iMac back to Apple, show them the issue, and ask them to check the machine.

 

[imacken]

Yes, I agree it's hardware.
Is the behaviour I describe consistent with what one would see if the GPU was throttling?

 

[h9826790]

Yes, I agree it's hardware.
Is the behaviour I describe consistent with what one would see if the GPU was throttling?

If it’s thermal throttling, the effect should not be that identical in almost all games, all setting, and in different OS. Also, as I said before, the throttling should go straight away after you quite the game (GPU cool down), no need to reboot.

The reboot requirement seems something crashed, and require complete re-initialisation.

 

[imacken]

I think you should ignore the reboot thing. That may not be required. Maybe just a period of inactivity.
The pattern could be the same as the games I play are all very GPU intensive, and looking at iStat after each session, the temps are over 100 degrees throughout.
I’m just trying to understand if the behaviour I describe could be consistent with throttling. I just don’t know!

 

[Kcetech1]

it could be throttling and then stuck in the throttled state, especially if you have upgraded to High Sierra where some of us still have issues on the dGPU's going back to speed after a throttle or an extended sleep period. But if its constantly 100c or high a dying GPU is a good possibility as well ( I killed 3 motherboards in the same machine by running the GPU hard doing 3D renders ), I would go in and get it checked especially if you still have Applecare and can easily replicate the issue.

 

[imacken]

Thanks again.
In normal use, the GPU is happily sitting at around 40 degrees. It's only in high intensive games that it hits over 100, and cools down immediately after. Hitting the 100+ in games has always happened since I bought this iMac 2 years ago, and I remember threads about that at the time saying 'not to worry about that, it's designed that way, and obviously the fans are doing their job.'
I'm about a 150 mile round trip to nearest Apple Store, so I'd like to be sure the trip won't be wasted before I go! I might call Apple support and see what they say.