I have a Mac Pro Mid 2010 with two ATI Radion 5770's driving 6 Dell U2412M's. Problem is, when even just one of these displays is rotated to portrait, the entire system grinds to a halt. CPU usage spikes to about 85%, I have 12gb of RAM installed and when this happens, about 512mb is free. And graphics performance is all but completely dead. At first I thought this may be because I am driving six monitors at once. But this is illogical be cause for one, it only just started occurring since I upgraded to 10.8(which as a power user, I absolutely hate). And two because this also happens with just one monitor hooked up. Any ideas?

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    Check the "Graphics/Displays" section of System Information. For a given display, does the "Rotation" line say "Supported"? I feel your pain about 10.8... – Thorgrim Feb 8 '13 at 15:56
  • I assume the monitor gives the on/off/on flash to black then back to normal again? this is not ideal, but a good test might be to turn a monitor off, unplug the display cable, make sure 10.8 knows it's gone, then rotate the display, and plug the monitor back in again. Of course Thorgrim's suggestion is the first step. – NOTjust -- user4304 Apr 16 '13 at 15:12
  • ok. just checked mine, MBP2012nR->U2211H->No longer auto-recognizes rotation. Must go sys prefs>displays>display(tab)>rotation(menu)>90-degress. Then, only 1080x1920 shows correctly (not clipped, or horribly stretched) (on ML). I tried with built-in display both on and lid shut (off). very different from <10.8! 1600x900 works fine in landscape, but is clipped on the left side so that I miss the apple menu and the application menu for long application names (my menu starts at 'references', as in System Preferences). Horrible! – NOTjust -- user4304 Apr 16 '13 at 15:22
  • Have you considered filing a bug since this might just be that… developer.apple.com/bugreporter – bmike Apr 30 '13 at 13:41

This is the sort of thing a well documented bug would let an engineer fix the code to avoid crippling a powerful Mac with a video change.

  1. https://developer.apple.com/bugreporter/
  2. Once you have the machine blocked, type sudo sysdiagnose in terminal and send that output in with the bug report as an attachment.
  3. Usually, you never hear back, but sometimes you'll get an email requesting more details to help engineering isolate the behavior you are seeing.

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