Re: Strange perfromance results on G4 and G5 FFT

• Subject: Re: Strange perfromance results on G4 and G5 FFT
• From: Chris Cox <email@hidden>
• Date: Wed, 13 Oct 2004 13:28:49 -0700
• Delivered-to: email@hidden
• Delivered-to: email@hidden

You did look for any cache hints that might have been put in for the G4, right?

dcbz = evil on the G5

Chris

I am benchmarking accelerated FFT's ( 512x512 real, using fft2d_zrip in vDSP ) and am getting some wierd results :

1Ghz single G4 ( codegen and instruction scheduling set for G4 ) 13msec
1Ghz single G4 ( codegen and instruction scheduling set for G5 ) 12msec
2Ghz dual G5 ( codegen and instruction scheduling set for G5 ) 17msec

When I launch two instances simultaneously on the dual G5, THey both finish in 24msec.

Does anyone have any idea why a 2x faster dual G5 performs slower than a G4 for a single instance and about the same for two instances ? This one has me puzzled.

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