I have been working on benchmarks for around 50 games and apps over the past week; a continuation of some of the work I did when the 2012 680mx iMacs were released two years ago. I am comparing performance on a myriad of metrics across the 2012 and 2014 fully loaded iMac models including release driver performance versus mature driver performance versus overclock performance at 2560x1440 and 4k/5k resolutions.
I seem to have hit a stumbling block that I cannot resolve and figured I would ask here for help before I post my results. While the 4k/5k performance in bootcamp and OS X isn't as bad as I thought it would be, the M295X iMacs are performing nowhere near where they should be, especially when it comes to 2560x1440 resolutions. There have also been several instances in which I experienced micro stutters that randomly dropped the framerate and performance to almost half of what it currently was for a split second. In fact, in a dozen or more tests, the M295X actually performed worse than the 680mx at standard clocked speeds. Literally an actually decrease in performance for something that should be blowing a two year old card out of the water.
However, I seem to have come across an issue with the Core clock throttling itself long before it actually should be. Everywhere I look it appears that the stock M295X is intended to start throttling at 105°C and until then, with all of the power options on Max, should run at an 850mhz Core clock. However, with a clean Win7 install, the M295X starts throttling itself literally seconds after use and almost as soon as it hits 70°. I can manually watch this using any of the various Core/Memory/Usage/Temperate apps in windows and you can see a perfect Cosine curve in the Core clock as it starts fluctuation in my case between 720Mhz and 762Mhz. (I have included a quick photo below). The clock always starts out at 850 Mhz, so I know these aren't underclocked, but I cannot find a way for the life of me to lock the clock at 850 or disable PowerPlay (which seems to be AMD's temperature based throttle.) The higher the temperature gets, the lower the clock runs, which makes this an absolute PITA for repeat benchmarks and my numbers are all over the place.
I would like to confirm this is also an issue under Yosemite, is there a GPU tool which can show a visual graph of clock speed against temperature that anyone knows about? I looked and the best I could find are just generic lists of core/memory speeds and GPU usage/temperate, but nothing that can show Core throttling.
I don't mean to be alarmist, but I have a feeling that these M295X iMacs may have a lowered temperate curve for enabling throttling, and if this is the case, we are getting nowhere near the performance that we should be getting. Losing over 100Mhz core clock is a huge hit to performance, not to mention as the clock throttles, the micro stutters that can manifest are extremely annoying.
Unfortunately, there is no way around it, heat is a tremendous problem with these new iMacs and I fear we have a gimped M295X because of it. Out of 6 generations of iMacs, 3 mac pros and 2 G5's, I have never had a computer that has hit 104°C after 7 minutes of playing a game or rendering 3D and this new iMac shocks me. I seriously question the longevity of these machines and from an engineering standpoint, nothing on the market right now is designed to run over 100°C continuously without failing. Once you add in dust, ambient heat during a non-winter season, and months of use, I would be surprised if these machines lasted longer than a couple years without essentially burning themselves out. We can debate the 'dream' 980MX vs. M295X all day, but Apple chose to get to market with a Retina iMac and the only option was a card substantially hotter than what it should be. The entire AMD 290 line has had heat as a controversy since their release last year. The problem is that the thermal envelope on these cards is too hot for the cooling that this iMac form factor has to offer. If the GPU sits at 104°C while the card is oscillating between 720Mhz and 762Mhz we know that there is no way in heck that we are going to get a natural 850Mhz core clock out of these cards. Even if we do find a way to stop the card from throttling and lock it at 850Mhz, it will likely far exceed the 105°C temperature and bring about instability. This is why I fear this issue has nothing to do with drivers and is probably hardcoded into the card BIOS.
I do not want to spoil anyone's fun; the screens on these iMacs are the best I have ever looked at bar none and an absolute dream to work on. Just the brightness and color contrast alone from not having a visible LCD gate separating the pixels is gorgeous. People with needs that won't tax the GPU won't have any issue to deal with and will LOVE this machine and its breathtaking screen. But heat and the throttling I have experienced is a big problem for anyone wanting complete performance. As it stands, is the screen worth a GPU that is only 3-5fps better than a stock 680MX, and worse than an overclocked 680MX? My heart is breaking, I would have paid anything for a 980mx
Thoughts?
I seem to have hit a stumbling block that I cannot resolve and figured I would ask here for help before I post my results. While the 4k/5k performance in bootcamp and OS X isn't as bad as I thought it would be, the M295X iMacs are performing nowhere near where they should be, especially when it comes to 2560x1440 resolutions. There have also been several instances in which I experienced micro stutters that randomly dropped the framerate and performance to almost half of what it currently was for a split second. In fact, in a dozen or more tests, the M295X actually performed worse than the 680mx at standard clocked speeds. Literally an actually decrease in performance for something that should be blowing a two year old card out of the water.
However, I seem to have come across an issue with the Core clock throttling itself long before it actually should be. Everywhere I look it appears that the stock M295X is intended to start throttling at 105°C and until then, with all of the power options on Max, should run at an 850mhz Core clock. However, with a clean Win7 install, the M295X starts throttling itself literally seconds after use and almost as soon as it hits 70°. I can manually watch this using any of the various Core/Memory/Usage/Temperate apps in windows and you can see a perfect Cosine curve in the Core clock as it starts fluctuation in my case between 720Mhz and 762Mhz. (I have included a quick photo below). The clock always starts out at 850 Mhz, so I know these aren't underclocked, but I cannot find a way for the life of me to lock the clock at 850 or disable PowerPlay (which seems to be AMD's temperature based throttle.) The higher the temperature gets, the lower the clock runs, which makes this an absolute PITA for repeat benchmarks and my numbers are all over the place.
I would like to confirm this is also an issue under Yosemite, is there a GPU tool which can show a visual graph of clock speed against temperature that anyone knows about? I looked and the best I could find are just generic lists of core/memory speeds and GPU usage/temperate, but nothing that can show Core throttling.
I don't mean to be alarmist, but I have a feeling that these M295X iMacs may have a lowered temperate curve for enabling throttling, and if this is the case, we are getting nowhere near the performance that we should be getting. Losing over 100Mhz core clock is a huge hit to performance, not to mention as the clock throttles, the micro stutters that can manifest are extremely annoying.
Unfortunately, there is no way around it, heat is a tremendous problem with these new iMacs and I fear we have a gimped M295X because of it. Out of 6 generations of iMacs, 3 mac pros and 2 G5's, I have never had a computer that has hit 104°C after 7 minutes of playing a game or rendering 3D and this new iMac shocks me. I seriously question the longevity of these machines and from an engineering standpoint, nothing on the market right now is designed to run over 100°C continuously without failing. Once you add in dust, ambient heat during a non-winter season, and months of use, I would be surprised if these machines lasted longer than a couple years without essentially burning themselves out. We can debate the 'dream' 980MX vs. M295X all day, but Apple chose to get to market with a Retina iMac and the only option was a card substantially hotter than what it should be. The entire AMD 290 line has had heat as a controversy since their release last year. The problem is that the thermal envelope on these cards is too hot for the cooling that this iMac form factor has to offer. If the GPU sits at 104°C while the card is oscillating between 720Mhz and 762Mhz we know that there is no way in heck that we are going to get a natural 850Mhz core clock out of these cards. Even if we do find a way to stop the card from throttling and lock it at 850Mhz, it will likely far exceed the 105°C temperature and bring about instability. This is why I fear this issue has nothing to do with drivers and is probably hardcoded into the card BIOS.
I do not want to spoil anyone's fun; the screens on these iMacs are the best I have ever looked at bar none and an absolute dream to work on. Just the brightness and color contrast alone from not having a visible LCD gate separating the pixels is gorgeous. People with needs that won't tax the GPU won't have any issue to deal with and will LOVE this machine and its breathtaking screen. But heat and the throttling I have experienced is a big problem for anyone wanting complete performance. As it stands, is the screen worth a GPU that is only 3-5fps better than a stock 680MX, and worse than an overclocked 680MX? My heart is breaking, I would have paid anything for a 980mx
Thoughts?
