From: Giuliano Pochini <pochini@shiny•it>
To: linuxppc-dev@lists•linuxppc.org
Subject: Re: [OT] 7450
Date: Mon, 12 Mar 2001 12:57:19 +0100 (CET) [thread overview]
Message-ID: <XFMail.010312125719.pochini@shiny.it> (raw)
>> 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
>speeds).
>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.
Bye.
Giuliano Pochini ->)|(<- Shiny Network {AS6665} ->)|(<-
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next reply other threads:[~2001-03-12 11:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-03-12 11:57 Giuliano Pochini [this message]
2001-03-13 5:56 ` [OT] 7450 Timothy A. Seufert
-- strict thread matches above, loose matches on Subject: below --
2001-03-09 8:59 Giuliano Pochini
2001-03-09 19:08 ` Dan Malek
2001-03-10 15:15 ` Holger Bettag
2001-03-11 1:43 ` David Edelsohn
2001-03-15 13:05 ` Holger Bettag
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