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 Posted: Jun 03, 2006 - 02:12 AM |
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Joined: Feb 22, 2002
Posts: 220
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"The OS is smart enough to "parallize" the operations, which windows does not due on a single CPU processor "
Neither the OS, nor the compiler need know much, if anything, about the X86's ability to simultaneously issue FP and integer instructions. If you have a mix of FP and integer instructions, the instruction scheduling hardware will execute them in parallel for you. It will also speculatively execute instructions on both sides of a branch, and discard those that get bypassed. Intel's compilers do try to keep the execution pipelines full by avoiding data dependencies that cause stalls.
The P4's SSE2 unit can do four FADDs or two FMULs per clock. While the integer units are calculating source and destination pointers and testing condition codes, the FP unit can be doing the math. All this parallelism is in the hardware. So if you were going to compute the average of an array of 32 bit numbers, you'd find it going faster if the numbers were floating point.
Of couse you can write a routine that runs poorly in FP, but the idea that FP is always slower is untrue, and as more emphasis is placed on FP performance, it will only get better. The PowerPCs AltiVec unit is a good example of FP being faster than integer. |
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Posted: Jun 03, 2006 - 04:03 AM |
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Joined: May 18, 2006
Posts: 142
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ScottKroeger wrote:
The P4's SSE2 unit can do four FADDs or two FMULs per clock.
Wow! Point taken, obviously been away *FAR* too long on where Intel's at. Last I knew they were no where near parity (about 50% as I recall).  And my programming habits obviously show it.
Seriously, can you refer me to some white papers so I can get caught up?
Man this place is *AWESOME*!  |
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Posted: Jun 03, 2006 - 05:28 AM |
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Joined: Feb 22, 2002
Posts: 220
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I don't have any white papers to recommend, but Ars Technica has been a good source of CPU architecture comparisons over the years. They've been keeping track of the relative merits of PowerPC and the various spins of the X86.
The rising importance of gaming is putting pressure in Intel to improve FP performance. AMD has the edge in gaming and Intel wants it back. It's nice to know that soon, the easiest way to slog through numerical algorithms (FP) will also be the fastest way, even if you don't code well. |
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Posted: Jun 03, 2006 - 06:11 AM |
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Joined: Sep 25, 2003
Posts: 2189
Location: Los Angeles, USA
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Quote:
I am using AT90CAN128 and using AvrStudio.
Long ago I lost the connection between this thread and the OP request. |
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