AM4_PCRATIO: A Frequency For Each Core!
Hiding behind this obscure name is a small utility allowing one core to be overclocked, or to set one CCX (CPU Complex) to a different frequency than the other one. If you don't know why you'd bother, allow us to explain in a little more detail.
When overclocking a processor, all of the cores operate at the same clock rate, and this is great for most folks. On the other hand, if you're gunning for a single-threaded benchmark record, performance is held back by the least-scalable silicon.
Take a quad-core processor as an example. Some of its cores are capable of running at 4 GHz, while others hit 4.2 or 4.4 GHz. Without utilizing special tools, you'll lock up as soon as you try pushing past 4 GHz since some of the cores aren't capable of going any higher. Talk about a frustrating situation: the best cores are held back by the worst.
The CCX Version
Using am4_pcratio_ccx (instead of am4_pcratio_focus) allows the frequency of all cores in one CCX to be changed, while the other CPU Complex's cores are automatically adjusted down to a lower clock rate.
Here is an example of three processors: A, B, and C. The value shown in blue indicates the maximum frequency that the cores are capable of operating at.
- A: In this example, whether you deactivate cores from the BIOS or from AM4_PCRATIO, you won't see much of a gain because they're all identical.
- B: Core 0 is the best one. You can can choose to uniquely activate it from the BIOS, while the others are turned off. With fewer active cores, the processor generates less heat and you can overclock even further. Another method would be to use AM4_PCRATIO with a focus on Core 0. The result would be roughly identical, but you'd end up with other active cores. For instance, Windows would run on some cores at 2 GHz, allowing the benchmark to have unique control of the fastest core.
- C: Now the fastest core is Core 3. It isn't possible to reserve only this one using the BIOS. So, using AM4_PCRATIO is your best chance for an improved benchmark score.
Given that each processor is different, it is difficult to quantify the gain from this manipulation. Worst-case, if you spend time trying each core and discover their limits are all the same, you wasted a couple of hours. On the other hand, if your sample is more like our second or third example, the gains can be substantial. Knowing that a competition can be won with a 10 or 20 MHz advantage, this is far from anecdotal.
Put your hard work in at room temperature. That'll allow you to conserve several liters of LN2.
With a bit of experience, it's easy to figure out the limits of individual cores quickly. All you need to do is overclock each one, raising their frequencies individually until your PC crashes. Since we have to run our benchmark multiple times, choose a 10- to 15-second test for brevity.
Our strategy was as follows:
- Start by finding the limits of Core 0, then focus on Core 0 by using AM4_PCRATIO and execute GPUPI.
- If the benchmark completes, note the stable frequency and proceed to a higher clock rate. Repeat this operation until the system freezes. We now know the maximum frequency for Core 0. If the test completes at 4000 MHz, 4025 MHz, and 4050 MHz, but fails at 4075 MHz, we conclude that 4050 MHz was the limit.
- Restart the PC and change focus to Core 1. If 4000 MHz is OK, but 4025 MHz causes a crash, Core 1 isn't as good, so we don't use it.
- Repeat this process across the CPU to determine its strongest core.
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