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| 15-12-08 / 22:31 : OSX 10.5.6 : Altivec 50% faster on PowerPC (cjed) |
| The MacOSX 10.5.6 update is finally available. We immediately notice that it is snappier (windows, minimizing), and after launching XBench (comparison with results from previous versions of Leopard) we discover that CPU performance is globally higher by 10 percents : in fact integer calculations (that count more and explain the 10% only increase) and vecLib FFT performances are the same, but floating point calcluations are 30% higher, and Altivec gains an even outstanding 50% increase, that gives it back the same result as with Tiger ! This last point was very important for audio applications, whose plugins use a lot Altivec (now abstracted APIs - targeted to Altivec on PPC and SSE on Intel - that were renamed Accelerate framework in Leopard). So there is no more reason to keep tiger for audio, and this fix demonstrates that Apple is aware of such details that plagged the old PPC under Leopard (there is to know if SSE4 instructions have also been used more efficiently in the Accelerate framework running under Intel). Quartz graphic engine performance remains the same (was still 10% more efficient than with Tiger), and the user test interface still shows the same previous hit over Tiger, a two times longer delay to display the controls under Leopard. As the Quartz engine isn't worse (is a little better), the reason is that Leopard puts more demand on it : windows shadows width have been at least doubled compared with previous OSX versions (in order to be more visible by Windows VISTA users - the laster added such over present effect). These shadows (dynamic) are computed by OSX with a huge precision (since the first version). Moreover the mirror effect used by Leopard Dock may add even more work (perhaps some precaching, besides the existing double buffering). When launching Safari it appears far more quick at opening windows and rendering pages. Apple may have updated the WebKit framework, or it might use the Altivec for some processing (that isn't intended for such task). The Finder (whose version is numbered aside) jumps from 10.5.6 to 10.5.8. |
| Comments |
In fact, as I read in the Cocoa Programming book some months ago (the text can be found here) Quartz can use Altivec for optimizing compositing, when an image buffer (NSImageRep) width is a multiple of the buffer depth (in bytes) : for example with a RGBA buffer (4 plans, then 4 bytes or 32 bits) if the width (in bytes) of the buffer (a tab) is a multiple of 4. So Leopard can benefit from Altivec for displaying windows shadows and Dock mirror effect. That should then explain why the 10.5.6 update can also be faster in that area. |
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