Thread-topic: Strange perfromance results on G4 and G5 FFT
I'm afraid my knowledge of ppc optimization is primitive compared to
yours.
What is dbcz and how would I change the distance and cacheline size for
read aheads ?
-----Original Message-----
From:
perfoptimization-dev-bounces+chris.bevis=email@hidden
[mailto:perfoptimization-dev-bounces+chris.bevis=email@hidden
ple.com] On Behalf Of Chris Cox
Sent: Wednesday, October 13, 2004 1:29 PM
To: Performance optimization list
Subject: Re: Strange perfromance results on G4 and G5 FFT
You did look for any cache hints that might have been put in for the G4,
right?
dcbz = evil on the G5
And you need to change the distance and cacheline size for read
aheads (dcbt) on the G5.
Chris
At 12:23 PM -0700 10/13/04, Bevis, Chris wrote:
>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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