TT030 Differences in FPU benchmark

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dexterslab
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TT030 Differences in FPU benchmark

Post by dexterslab »

after all these benchmarks i seem to keep doing i've previously noticed a difference in FPU performance between different TT machines...

my original TT which is an early spec one usually benchmarks at 102% for FPU in Genbench against a stock TT. The TT i bought last year is a late spec one but only benchmarks at 85% which is a difference between the two machines of 17% which is a significant shortfall.

I usually expect some slight changes in benchmarks between machines, maybe 1% or something... but i'm surprised by 15% too slow!

This only seems to affect the FPU performance, using Gembench all the other tests seem to be within 1%

Has anyone else seen this?

Anyone know what might cause it? - AFAIK the CPU and FPU are run from the same clock source in the TT so if it was a slow clock i'd see the CPU performance low as well...

:coffe:
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Re: TT030 Differences in FPU benchmark

Post by Frank B »

dexterslab wrote:after all these benchmarks i seem to keep doing i've previously noticed a difference in FPU performance between different TT machines...

my original TT which is an early spec one usually benchmarks at 102% for FPU in Genbench against a stock TT. The TT i bought last year is a late spec one but only benchmarks at 85% which is a difference between the two machines of 17% which is a significant shortfall.

I usually expect some slight changes in benchmarks between machines, maybe 1% or something... but i'm surprised by 15% too slow!

This only seems to affect the FPU performance, using Gembench all the other tests seem to be within 1%

Has anyone else seen this?

Anyone know what might cause it? - AFAIK the CPU and FPU are run from the same clock source in the TT so if it was a slow clock i'd see the CPU performance low as well...

:coffe:
Do you have a 68882 or a 68881 installed?
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

yes, both have MC68882FN33A as standard
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Re: TT030 Differences in FPU benchmark

Post by wongck »

It goes to hog mode on one :mrgreen:
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Re: TT030 Differences in FPU benchmark

Post by Frank B »

dexterslab wrote:yes, both have MC68882FN33A as standard
Please try the following on both machines in a 16 colour screen mode. TT high or ST low and see if the results differ.

Frank
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

thanks frank, i'll give it a try... now i just need to put my other TT back together :oops:
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

TT #1: 20.182
TT #2: 30.107
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

just run nembench on them:

The 'slow' TT

Code: Select all

Float multiply (64bit)       -> 0.270 MegaFlops (~101%)
Float divide (64bit)         -> 0.175 MegaFlops (~101%)
Linear (stalled) float       -> 0.528 MegaFlops (~99%)
Interleaved (piped) float    -> 0.564 MegaFlops (~106%)
The 'normal' TT

Code: Select all

Float multiply (64bit)       -> 0.541 MegaFlops (~204%)
Float divide (64bit)         -> 0.351 MegaFlops (~203%)
Linear (stalled) float       -> 1.006 MegaFlops (~188%)
Interleaved (piped) float    -> 1.003 MegaFlops (~188%)
Which given this is ref a Falcon, i'm wondering if the FPU is running at 16Mhz instead of 32... and i'm pretty sure i remember a jumper on the TT motherboard to switch between 16/32mhz, i think it's time i went and had a look for it!
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Re: TT030 Differences in FPU benchmark

Post by Frank B »

dexterslab wrote:TT #1: 20.182
TT #2: 30.107
Yup something doesn't look right :) I should post the integer fp emulation one too so you can see what a difference it makes on compiled code. The fpu one is 22x faster :) I should probably stick a UI on the app too.

Frank
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

yep, jumper set to 16mhz! :evil:

had to take out the VME slot and everything to get to it

wonder how long it's been set like that! could have been years!

I've also corrected the results in the NemBench thread that i posted into a month or so ago

Code: Select all

NemBench v2.1 - precision CPU/FPU profiler.
Float multiply (64bit)       -> 0.541 MegaFlops (~204%)
Float divide (64bit)         -> 0.351 MegaFlops (~203%)
Linear (stalled) float       -> 1.006 MegaFlops (~188%)
Interleaved (piped) float    -> 1.003 MegaFlops (~188%)
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Re: TT030 Differences in FPU benchmark

Post by jvernet »

Do you have a picture of this jumper ? I will do the test on my own TT to see if the FPU run à 16 or 32Mhz.
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

no sorry... but it's a standard 3pin header with a jumper, on the early boards it's right above the FPU IC. On my newer one it's just above the VME connector close to the 32mhz oscillator. It's labelled 'W101'
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Re: TT030 Differences in FPU benchmark

Post by wongck »

So did you notice any slow down when it was set to 16MHz or you only notice it in the benchmark numbers?
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Re: TT030 Differences in FPU benchmark

Post by dexterslab »

just in the benchmarks... not many apps use the fpu of course
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Re: TT030 Differences in FPU benchmark

Post by wongck »

Yes, not many apps use it.
better check my TT :wink:
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