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The Performance Edge: How Much Of A Difference Do Dual Processors Make? It's Mixed - The Dual Processor G4/800 Meets Mac OS 10.1
Thursday, October 11, 2001

We have done preliminary performance testing on the new Quicksilver dual G4/800 and single G4/867 running Mac OS 10.1, and thought we share the results with you. Like the 867 MHz Quicksilver, the 800 MHz machine has 256K of on chip L2 cache running at full processor speed, and 2 MB of L3 cache running at 1/4 the processor speed. In the case of the 800 MHz machine everything is doubled. (L3 cache sits between the processor and main memory.)

OS X is supposed to be built from the ground up to take advantage of dual processors. Once you are running a Carbon or Cocoa application, we are told, you should see a significant performance improvement. From our testing that has indeed been the case with parts of some programs. The programs we used for testing are heavily weighted towards applications developed by Apple. We felt that these programs would be the most up-to-date applications in terms of taking advantage of the G4 processor and also dual processor configurations.

As you'll see from the results below, performance of the dual processor machine is really mixed. Converting a QuickTime movie to a DV Stream showed an 80% speed improvement for the dual processor Power Mac. However when encoding the same file using a Sorenson codec, the dual processor machine was slightly slower than the single processor 867 MHz. So we are puzzled why we are getting good results in one instance but poor results in the other.

Many of the other test, also showed no performance improvement.

However you can see the potential in a dual processor setup by viewing the AltiVec fractal results. If you adjust for processor speed, the dual processor machine was almost twice as fast. This test completely saturates the processors with data, and you can see how this could be an advantage to people that do the type of work on their computers that calls for huge amounts of continuous data crunching.

We have contacted Apple for input on helping to explain why we are getting these varying results. Of particular interest is why we are seeing no improvement in the iTunes, QuickTime (Sorenson codec) & iMovie Effects, when running under a dual processor environment.

We would also welcome reader input about these curious results and suggestions for other applications we could use to stress dual processor setups, Mac OS X, and the G4.

Take a look at the results below. We have included our best guess about what is going-on to generate these differences. If you have a better explanation, or a different opinion, please let us know. Either e-mail us, or use this link to post your ideas on our bulletin board.

All machines were configured similarly and running OS 10.1

Note: This is our initial look at the performance of the new Quicksilver Towers. We will be running more tests and hope to have a full review of all the new Power Macs in the next few weeks.

Additional resources:




"Real World" Tests

The tests below are from our suite of real world application tests. These tests feature a diverse selection of applications commonly used by the Mac community. The test suite was designed to render an accurate and well rounded picture of a machine's performance. All of the tests below were timed with a stopwatch. The times are then converted to percentages relative to the Quicksilver 867 MHz machine which is set to 100%. For all scores, higher numbers are better.

QuickTime Tests

Although a Sorenson encode responds well the Velocity Engine function of the G4, it does not appear able to take advantage of dual processors

This is the kind of performance we would expect from a dual processor setup. There is some overhead, and so in most cases you do not see a doubling of performance

The drive performance is probably more of a factor here but not totally. It seems that having an extra processor is of no advantage when carrying out this type of function

Only modest improvement in performance for the dual processor machine. We noticed that neither processor was fully utilized when carrying out this operation. Indeed, only about 1/4 of the processing power of each processor was being used. It is hard to believe that this was because of the inability of the hard drive to keep the processor fed with data. The file used for this test was 320 MB in size.

Dual processors show no advantage. Bottleneck may be the SuperDrive performance

 

Dual processors have no effect, speed of processor does

The Search & Replace function also does not seem to be able to utilize dual processors

Ok, this is what is suppose to happen with a Carbon or Cocoa application when running under OS X

This test is completely processor intensive and both processors in the dual machine were continuously flooded with data

This test opens and closes 1,000 windows as fast as possible. No benefit to having a dual processor here

These results mirror the performance differences we observed between the two machines when running under OS 9.2

 

This again was about the same under 9.2

 

In this test several applications are opened and closed repeatedly using AppleScript. The better performance of the dual processor machine may be due to better drive performance rather than the fact that the machine has two processors



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