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I am writing a cross-platform OpenGL application and I am experiencing very different performance results between OS X and Windows (both 7 and 8).

In Windows GPU-Z reports the Sandy Bridge HD 3000 GPU continues to run at 350Mhz no matter what, and this would explain to me why my code seems to execute something like 5 times faster within OS X than in Windows.

To verify this, I thought it would be nice to verify that the clock speed is indeed getting ramped up in OS X but there is no GPU-Z for OS X.

Any ideas?

Another way for me to put this issue to bed is to figure out how to get the IGP to correctly spool up under Windows. I have just tested sketchfab in Chrome, which has it hitting a nice full 1200Mhz on the TIE fighter model (and I was surprised at how well it scaled to GPU demand: less complex models had the clock set at 650 or 750Mhz. Pretty neat.)

Okay. So Chrome has something implemented right that I don't. Perhaps it's time I stopped using SDL. Now I've got to figure out how to get it to hit 1200Mhz when running my program.

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I have been able to get the clock speed to go up with my program! It does so quite sporadically because my graphics load is very low most of the time. If I put a more constant load (some more heavy duty shading) I will surely get more consistent timing data once the clock speed gets pegged to max.

This is actually really really neat, though, because it means my program is so well-optimized that it can keep the GPU idle long enough for throttling to occur. When I eliminate the sleep calls in my program (so the simulation runs much faster than real-time) I am now able to keep the GPU clock at 1200Mhz. It seems like a reboot (and running the release version of the build) helped it adjust.

Update: I solved what was the problem I was dealing with but I did not come to a satisfactory answer for my original question which is how to check the realtime clockspeed of an Intel Sandy Bridge IGP on OSX. Can anyone help me with this? (Apple engineers maybe?)

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In Linux it's in /sys/kernel/debug/dri/0/i915_max_freq – Andrew Smith May 13 at 16:40

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