Articles: CPU

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Test 3: Real Game Test

The so totally different results of the first two tests made us delve deeper into the specifics of CPU benchmarking in Doom 3. And we realized that it was wrong to measure the CPU performance in Doom 3 using pre-recorded demos because the results wouldn’t reflect the real game process. The problem with the demo records in Doom 3 is in their not containing only the player’s actions but also the reaction of the outside world and the monsters to these actions. That is, part of the load that exists in real play is removed from the CPU when it is just playing a demo back. The CPU does skinning, shadows and tangent space transformations, but does not do the monsters AI and the physics modeling of the world when playing a prerecorded demo. So, the results we got in the two above tests as well as the results of many other reviewers can be justly called into question.

We had to do without demos to measure the real performance of CPUs in Doom 3. So we played the game for a while looking for moments when the CPU was under the highest load. First of all, we’d like to remind you that the rendering speed has a ceiling of 60 fps in Doom 3. In other words, there’s no sense in going for a faster processor if your current one can maintain an fps rate of 60. As we found out, the fps rate with the Medium Quality settings and with a powerful graphics card rarely falls below 60, i.e. CPU models with 3GHz and higher frequencies or 3000+ and higher ratings guarantee an acceptable performance.

However, you may sometimes experience a slowdown when the CPU is incapable of rendering those 60 frames in a second. This usually happens when there are many monsters in the same room with the player – calculating skinning and AI for the monsters puts too heavy a load on the CPU. This observation led us to the right method of measuring the CPU performance in Doom 3, in real gaming conditions.

The point of our method is in arranging a get-together of a lot of monsters in the same room and measuring the fps rate with the Fraps utility. Again, we returned to the Central Server Banks on the CPU level. Having turned on the “immortality” with the god command and having run a couple of circles around the level, we managed to get together a score or more of monsters of various kinds and characters. We then saved the game and read this save file on each of the tested systems to compare their performance in real game conditions and in one of those moments when the CPU has to crunch through a huge amount of calculations, rendering skins and shadows, modeling AI and physics. We were measuring the fps rate for three minutes and within this interval half of the monsters had killed the other half, releasing the speed to the ceiling of 60 fps. We do assert that the results we got this way allow for a more correct comparison of CPU performance in Doom 3.

First of all, here are the minimal fps rates we got with different processors:

As you see, the speed can drop much below the 60fps ceiling – some processors even get below 30fps, which is the empirical minimum, necessary for a comfortable play.

The overall picture is typical: we can’t name a definite winner. The loser is certain, though. The Athlon XP family suffers a fiasco in this test.

The results explain where the recommendation to have a processor of 3GHz frequency or 3000+ rating comes from. Note also that the Pentium 4 3GHz work faster than the Athlon 64 3000+ or even the Athlon 64 3200+. However, the top-end members of the Pentium 4 and Athlon 64 families have similar results.

And here are average fps rates for the same test:

The overall situation remains the same: the Athlon 64 models line up in order of their ratings. The Prescott-core Pentium 4 models are faster than their Northwood-core mates, the frequency being equal. The i875P platform turns to be faster than the i925X Express.

So, our “right” testing in Doom 3 suggests that there’s no CPU architecture best suited for this game. The results we got with demo records produce quite another picture, though, and that means the ordinary timedemo method is not the best or correct way of benchmarking CPUs in Doom 3.

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