Author: Albert Silver
Date: 21:08:14 03/03/00
Go up one level in this thread
On March 03, 2000 at 22:16:39, Robert Hyatt wrote:
>On March 03, 2000 at 20:05:57, Tom Kerrigan wrote:
>
>>On March 03, 2000 at 17:08:58, Robert Hyatt wrote:
>>
>>>Problem is the compilers don't know what is going on. IE how many "hidden"
>>>registers does the architecture have for renaming? Intel (nor anyone else)
>>>will make this a 'constant'.
>>
>>But my point is, why have register renaming at all. I can list a dozen good
>>processors that don't do it. I would like to know the exact percentage speedup
>>it gives you.
>
>
>That is probably lost in the benchmark data. But in the case of intel, with
>8 (barely) usable registers, it would be impossible to keep multiple pipes
>busy due to register conflicts. Renaming solves this nicely and frees up
>parallel streams of instructions to keep the pipes busy...
>
>Some don't need to do this, like the sparc/ultrasparcs, because they have
>32 accessible registers for programming. But 8? What a decision... :)
>
>
>
>
>>
>>>And how does the P5 do more per cycle than a P6 when the p6 can do three
>>>ops/cycle, while the P5 drags along at a max of 2, and it requires a very
>>>good compiler to do two at a time???
>>
>>TSCP (1.42) on an original Pentium/200 searches 136 NPS/MHz.
>>
>>On a Pentium II/300, it searches 119 NPS/MHz.
>>
>>So the Pentium appears to be 15% faster, despite its lack of out-of-order
>>execution, branch predition, speculative execution, register renaming,
>>reservation stations, blah blah blah.
>
>
>That looks like a compiler issue. I ran crafty on a P5/233mmx, and a P6/200,
>and the P5 was about 70% as fast (I have a P5/233 notebook laying around,
>and while it was not bad, it was definitely slower than a p6/200 machine
>for all the things I tested (ie linux kernel builds, crafty testing, etc.)
>
>
>
>
>>
>>I assume this is because the P5 has shorter pipes and doesn't have to flush them
>>all the time due to speculative execution gone wrong.
>>
>>(BTW, the K5 has almost everything beat. It searches 173 NPS/MHz, and it doesn't
>>do anything particularly fancy either.)
>
>same point as above. For crafty, the K* processors are slower. I have not
>delved into why...
>
How about on the Athlons?
A.S.
>
>
>
>>
>>-Tom
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