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之所以在这里说了这么多，其实主要还是觉得，过去时我们能简单通过管线数目、显存带宽、辅助晶体管数目就能大致推测一个显卡的性能。
而到了DX10时代，这个标准确变得很主观 很模糊 很难把握：
1. 没有测试，我们什么都推测不到。
2. 同样硬件，一个驱动就是天翻地覆的变化，"神 - 油"背后到底干了什么。
3. 厂家越来越喜欢玩弄概念，没有解决实质的问题而单单喊了很多口号，我们是否有必要为这些概念买单。
不只是我一个人关注这个问题。
http://www.equn.com/forum/viewthread.php?tid=18626&page=1#pid248708
看到一个有意思的回复：
Hi All,
I read a debate going on in the forums as to why ATI core is givingless PPD compared to NVIDIA core. And I see many reasons givenincluding the wu's assigned are different (Definitely that also willimpact) as well as MAYBE NVidia core is NOT DOING Science work justCredit work (ONLY possible if someone has goofed up major whileProgramming - LESS LIKELY because I am sure lot of testing has occuredwithin fah stanford group before releasing the GPU beta to the world.)
For a long time (From the time AMD and NVIDIA came out with Unifiedshaders) I have had a thought in my mind, which seems to be playing outnow if the PPD results are valid (i.e no programming error some where).So let me start =>
EVERYONE has to REALIZE the difference in definition of SPs betweenATI/AMD and NVIDIA. To be frank I would say the way ATI named theirsingle SP has SP is a kind of JOKE (in some ways) compared to NVIDIA.
Based on what I have read about the NVIDIA and ATI GPU Architectures onthe Net (Haven't had time nor a ATI card at hand to write code toverify this yet)
IN NVIDIA __EACH SP__ is capable of doing either FP32 or Integer (ALL ops) or Special_functions.
WHILE
IN AMD __FOR EACH Group of 5 SPs ONLY ONE SP__ can do FP32 orInteger_MUL or Special function, while the other 4 SP can only doSIMPLE INTEGER operations.
So if the code is doing lot of FP operations or special functions orInteger_MUL IN EFFECT one gets only 1/5 th the number of SPs in ATI ascompared to what ATI claims as SPs i.e A ATI chip with 320 SPs is ineffect ONLY 64 SPs. So obviously a ATI performance will be only 50%compared to NVIDIA in the WORST CASE.
However in practice one would find that ATI GPUs will give bit moreperformance than the WORST CASE Mentioned above because IF one can mixthe FP32/IntegerMUL/Special_Functions with Simple_Integer ops then theother 4 SPs out of the 5 SP group in ATI can be utilized. Thusimproving over the WORST CASE which I mentioned.
SO BEFORE JUMPING AND CONCLUDING may be WE have to think of the realityinterms of what is ATI 320 SIMPLE SPs worth compared to NVIDIA 128 FULLSPs.
Note: Also one more thing which can aid ATI a bit could be the betterbranch/thread (i.e independent code) granularity in ATI compared toNVidia. But still the 128 Full SPs in NVidia vs 64 Full SPs in AMD/ATImay not help much for ATI wrt this granularity if the Vector sizes onwhich the operations are occuring are large.
Just my thoughts. Happy to get constructive feedback, even to theextent of telling that my thoughts are rubbish, provided it is backedtechnically. I am starting this thread mainly to understand the G80/G92core VS R600 core architecture/programming advantages/disadvantages.
Keep
HanishKVChanishkvc
这个人的推测倒是告诉了我们一个简单的换算公式，按照AMD的设计，如果继续把SP数目作为硬件指标进行对比的话，AMD和NVIDIA的实际比值是5：1
也就是说
3650的实际SP是120/5 = 24 对应 8600GT的SP数目为32 8500GT是16，3650性能刚好在两者之间
3850的实际SP是320/5= 64 对应 9600GT的SP数目为64，3850性能刚好类似于9600GT
4850的实际SP是800/5=160 超过了8800GT的112，8800GT完败，也超过了9800GTX的128，确实打得标准版的9800GTX无还手之力 只有推出超频版的9800GTX+来对抗
很有趣的是很现实的计算方法。 |
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发表于 2008-6-22 01:50
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