[OT] 7450

Giuliano Pochini pochini at shiny.it
Mon Mar 12 22:57:19 EST 2001

>> Giuliano Pochini wrote:
>> >
>> > I read many msg about 7450 performance problems.
>> From who?  People that are actually running hardware or
>> speculating from rumors based on documentation that doesn't exist?

>There are some Mac benchmarks flying around, which don't make the 7450
>look all too good.
>But at least one issue remains, and that is surprisingly low FP performance.
>This was measured with one ray tracing application and with an MP3 coder.
>I currently believe that thus far, no PPC compiler has made much effort
>schedule FP operations. With just three cycles of latency for a
>multiply-add, you can get away with rather sloppy code (in fact, I know
>of no shorter FPU pipeline in any other CPUs that reach comparable clock

>But with five cycles of FP latency, scheduling becomes really important.

Hmm, probably soft compiled for 604 runs fine on 7450 because it had
similar latencies and a 6-stage pipeline.

>> > .... Will GCC have optiminazions
>> > (workarounds?) for the 7450's longer pipeline ?
>> People are working on it.

>These aren't really "workarounds". Nowadays CPU architecture and compiler
>capabilities have to be regarded together. It may well be the case that
>the chip designers made a sound decision to move certain complexities to
>the software side rather than to the hardware side.

Yes, but it's not a good thing. People cannot recompile their software.

    Giuliano Pochini ->)|(<- Shiny Network {AS6665} ->)|(<-

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