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PPC 7457 performance tweak for new PowerBooks System
[robg pre-adds... Before you contemplate trying this hint, please read the comment with the tech note explaining why you should not do this. I'm leaving the hint in place as a warning in case someone finds the info elsewhere and wants to see what macosxhints might have to say on the matter.]

On my new PB15 (7457-based) I discovered that the Branch Target Instruction Cache is disabled. It was enabled on my prior Ti-Book (7450-based). I don't know why it's not enabled, perhaps the OS (10.2.8) still does not recognize the newer chip fully, and is playing it safe. Turning it back on does not appear to cause system instability, and increases performance slightly (3% on integer-intensive benchmarks).

The easiest way to turn the bit back on is to download the latest CHUD performance tools (3.0.1) from Apple, run the Reggie SE app, click the HID0 tab, then look for bit #26, BTIC. I don't know how to keep it on between reboots, though.

Be careful with Reggie SE. Random clicks in that tool are a sure way to lock your system up.

[robg adds: It took a bit of digging on Apple's site, but I finally found (on the Performance page of Apple's Developer site) a download link that will mount an FTP server in the Finder. The 3.0 version is a 21mb download. Anything that may not work on your machine after tweaking it in this manner is, of course, your own responsibility.]
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PPC 7457 performance tweak for new PowerBooks | 2 comments | Create New Account
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Updating to 10.2.8 problems and solution
Authored by: joang on Oct 15, '03 11:09:56AM

Updated to 10.2.8 - restart brought several problems: No date, monitor settings did not show up on the top bar. Opening1\0\05{\0\0\0\0\0\0\0\0t hold when clicking those preferences. Not only that, but I use Dock Extender ... it showed up with no icons, and all the devisions of each section were gone at well. Bummer, totally!

Trial and error worked here. Restart twice! The first time I restarted, the preferences were fixed back to the way they used to be - at least the date showed up. The monitor setting was back to ability to be chosen, show up, and stay there.

Restarting the second time fixed Dock Extender. Now, everything is back to normal.

I wrote Dock Extender Tech ... they verified that 1 other person had written in with the same problem, same solution.

Hope this helps if someone updates OS X., then goes into a panic over problems that show up with first restart.

Joan

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Webbuild Design
inexpensive web design and site maintainence



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PPC 7457 performance tweak for new PowerBooks
Authored by: persson on Oct 15, '03 11:37:37AM
The following is taken from the "G3 and G4 Processors and News..." forum in the Mac Achia of the ArsTechnica forums. It sure seems to me that at face value it indicates you should re-disable the BTIC if you want a stable machine!

I was unable to find this described in the errate for the 7457 on Motorola's website.

muscou Smack-Fu Master, in training Registered: September 26, 2003 Posts: 2

posted October 13, 2003 10:37

A few comments about the latest 74x7 errata( see bottom of post)

Does the 1.5% average performance hit suggested by Motorola can be corrobated by somebody on this forum using a few applications.

How can they let a bug like this one go through on what is supposed to be only a die shrink!!

Error No. 20: BTIC must not be enabled by software

Overview:

Enabling the Branch Target Instruction Cache (BTIC) of the Branch Processing Unit (BPU) of the processor will result in the attempted execution of corrupted instructions.

Detailed Description:

The BTIC is a 128-entry, four-way set-associative cache that contains the most recently used branch target instructions (up to four instructions per entry) for b and bc branches. When a taken branch instruction of this type hits in the BTIC, the instructions arrive in the instruction queue a cycle sooner than they would arrive from the instruction cache. Due to an error in the processor, the BTIC may provide corrupted instructions and should not be enabled. The BTIC is enabled in software by setting HID0[BTIC]. The default state of the BTIC is disabled.

Projected Impact: Symptoms of processor failures when HID0[BTIC] is set include unexpected exceptions, including but not limited to instruction cache parity errors. The performance of the processor is impacted if the BTIC is disabled. The actual impact is code-dependent but is anticipated to be between 0% and 3% on typical code streams (compared with. the performance of a processor with a functioning BTIC), with an average of 1.5%.

Work Arounds: None. Do not set HID0[BTIC] = 1.

Projected Solution: Under review.

Link to ars forum quoted above

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