From: Rob Baxter <robb@phx.mcd.mot.com>
To: linuxppc-dev@lists.linuxppc.org
Subject: PPC 7455 bogomips calculation
Date: Fri, 3 Jan 2003 16:26:47 -0700 [thread overview]
Message-ID: <20030103162647.A25677@phx.mcd.mot.com> (raw)
Hello,
I have a PPC 7455 based system running a 2.4.19 kernel. I would
like to know what others are seeing, as far as the bogomips calculation,
on other PPC 7455 based systems.
I'm seeing a bogomips calculation that is equivalent to the processor
core frequency. With systems based on pre 745x PPCs, normally one
would see a bogomips calculation of twice the processor core frequency.
I understand that it's just a calculation and not a benchmark and/or
performance measurement. I'm trying to understand why it's half of
what we have been seeing.
The delay loop that is utilized is this:
.align 5
_GLOBAL(__delay)
cmpwi 0,r3,0
mtctr r3
beqlr
1: bdnz 1b
blr
After some review of the PPC 7455 user's manual, it looks like the
branch prediction logic has changed a bit from earlier versions
(e.g., PPC 750, PPC 7400, PPC 7410). This may account for the difference
in the bogomips calculation.
Rob Baxter
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next reply other threads:[~2003-01-03 23:26 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-01-03 23:26 Rob Baxter [this message]
2003-01-04 1:01 ` PPC 7455 bogomips calculation Holger Bettag
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