Emulator

Just occurred to me that this might also be helpful information.

Nvidia Web Driver: https://www.dropbox.com/s/pdeqjthd4gw01ly/Screenshot%202014-08-02%2001.56.15.png

Try turning off vsync.

Vsync wasn't on. I only have the Framelimit to Auto, however changing that does not solve the problem.

If you hit tab during the half speed, does it have any affect? I'm wondering if this isn't a problem with OSX's iffy drivers.

After reproducing the problem a few times, both in windowed mode and fullscreen, hitting Tab seems to have no effect. I've tried hitting it once and waiting, and mashing it with no observable difference.

What is the internal resolution set to in enhancements?

I've tried playing at Auto (Window Size) and Auto (Multiple of 640x528) and neither affect it from what I can tell. Though from letting it run in the background, I've noticed if given enough time, it will go back to full speed, but again given enough time it will go back to half speed. And the cycle seems to be somewhat consistent in time between full speed and half speed.

Okay, what I'm going to guess is that auto is raising the internal resolution when you go into full screen, and eventually your CPU or GPU is getting to a temperature thresh hold. When it does, it lowers the clock rate, and the game lags. By leaving full screen, the window gets smaller and the internal resolution drops, speeding the game up and putting less stress on the components. Try running at 1x IR in full screen and seeing what happens.

My CPU and GPU are barely stressed out at all. I monitored my system throughout the full speed/half speed cycles, and my CPU/GPU was no more stressed during either of the cycles, nor were the temperatures any different. RAM usage was also unaffected. No thermal thresholds are being hit, my CPU only throttles when I am in the 90C+ range.

Here is a screenshot of Dolphin with Twilight Princess in windowed mode at 1x resolution (fullscreen didn't affect it) with HWMonitor on the right side showing all of my temperatures.

https://www.dropbox.com/s/pkmthlbhu7epa1c/Screenshot%202014-08-02%2003.28.21.png

It looks like vsync is being forced on by the drivers or osX.

I'm not a mac user, but there is apparently something called BeamSync which need to be disabled, ask google.

I think it's vsync being set by the driver then; that's the only reason option. I can't really help because I don't know much about mac's driver setup.

I've played with BeamSync before, however disabling it makes core animations chuggy and buggy, but has no affect on Dolphn. There is noticeable tearing when the game is running at 100%, it's not enough to get annoying, but enough to know that vsync isn't activated. From how I understand it, BeamSync only affects OS X's core graphics animations, so it theoretically shouldn't have an effect on Dolphin.

I could be wrong, however the problem persisted when I enabled Vsync with and without BeamSync enabled. There definitely wasn't any screen tearing this time around with Vsync enabled, but when I enabled Vsync though, the cycles no longer happened, the only way to fix it was to switch to/from fullscreen.

If Vsync was being set by the driver, wouldn't it always be stuck at the monitor's refresh rate and not be allowed to go to 120FPS for example?

When I have time to install Windows again, I will test it out as soon as I can to see if I can reproduce the effects there as well.

Does your gpu fall into low power mode perhaps? Also have you enabled the hyrule field patch using the latest development version(it affects all the game unlike what it says)? Set your gpu to high performance mode if you can with your mac.

My CPU and GPU are barely stressed out at all.

It's important to remember that Dolphin is not a very well multi-threaded application, it will at most only utilize two CPU cores. So even when Dolphin is reaching the bottleneck in CPU performance this would still only be displayed as 25% usage on an i7 with HyperThreading.

Yes, I made sure to have the Hyrule Field Patch on.

I was also monitoring my CPU and GPU clock speeds while playing Dolphin, and my GPU's clock speed doesn't change, however it also isn't at it's highest power state either when playing. My CPU ramps up to it's highest clock speed during emulation however.

To my knowledge, I don't think I can manually put it into any high performance mode, but I don't think it's changing power states since the clock speed for the core and memory don't change at any point.

I don't have this problem in any other place in Twilight Princess (at least that I know of yet up until this point) nor in any other game that I've played.

My CPU and GPU are barely stressed out at all

In OS X, it counts each thread as 100%, so I have 12 threads (6 cores hyper threaded) meaning it is out of 1200%. When in that room, it varies between 140% and 160%, but the CPU usage seems unrelated to when the lag occurs. My core temperatures are also fine, so no thermal throttling there.

Try turning up some of the enhancements like anti-aliasing to force your GPU into a higher power state.

Also, just because you're at 160% doesn't mean that one core is maxed. Dolphin could be making out the GPU or CPU thread, even though the other one isn't maxed out. Twilight Princess is extremely demanding.

After turning up the graphics settings, I couldn't make it go any higher except for one instance it went up by a few dozen MHz, but not for long enough to really matter.

Though after leaving it for a while, I noticed two cases of when it went through the cycle my GPU core went down by 200MHz, and another two separate instance where my GPU's memory went down to 1.2GHZ from 6.01GHz. It's possible that the other times it happened so quickly that the monitoring software didn't pick up on it.

The problem seems to stem when my GPU's memory clocks down to 1.2GHz for an unspecified reason. My guess would have to be Nvidia drivers, and from what I read on the Driver Comparison blog post, Nvidia drivers deem Dolphin as unimportant and don't give it proper resources.

Though these are just my observations, I could be totally inaccurate.

Also, just because you're at 160%...

I'm aware, in fact I decided to see which threads were being taken up by Dolphin, and it seems Dolphin was actually using 3 threads, 50% each. I'm not sure if that is possible considering I thought it could only use two threads, but perhaps it can only use 2 cores but maybe an additional thread on the same core?

Well, after one final test to see if it was a problem with the drivers: it was.

Nvidia's Web Drivers (their third party ones that don't come with OS X) were actually the culprit behind this. I switched to Apple's Nvidia drivers and it works much better. My GPU is running at its full 1.2GHz like it should be, my GPU memory is running at its full 6.01GHz like it should be, and never drops. The half-speed/full-speed cycles no longer happen, and overall everything is much smoother.

I believe the entire issue has been solved by reverting so Apple's drivers, and maybe a disclaimer for Mac users should be posted somewhere that the Nvidia Web Drivers will cause performance problems.

Thanks for helping and hopefully this will also help other users who have similar issues.