AMD Ryzen 9 3900X CPU Review

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3rd generation Ryzen CPU’s share several things in common with their predecessors. In fact, overclocking is largely the same in most respects. The Ryzen 3000 series supports overclocking in one of three ways. Manual, Precision Boost 2, and Precision Boost Overdrive. We will talk a little about each of these methods and how they differ, as well as explore the potential of our test CPU and what you might expect overclocking one of your own.

Precision Boost 2

Precision Boost 2 or “PB2” is basically a form of automatic overclocking. It’s an opportunistic algorithm which tries to increase the clock speeds of loaded cores within specific limits. It does not overclock a single core or all cores specifically. AMD’s literature on the matter is quite clear on the subject. However, this is more or less how it looks unless you watch everything in real time using something like the Ryzen Master software application which we will talk about as well. Essentially, the only real limitations are imposed by four things. PPT, TDC, EDC and the OEM boost clock. The OEM in this case being AMD. The processor for example may have a preprogrammed limit of 95A TDC and a 140A EDC. It will therefore modulate its clock speeds to stay within those ranges. Its sort of like a rev limiter for your CPU. If it hits the limit, it retards the clockspeed to stay within its default thresholds and do so until the situation changes. It analyses these conditions once every millisecond.

To understand what PPT, TDC and EDC are, it’s just easier to cut and paste from AMD’s literature:

1.Package Power Tracking (“PPT”):The PPT threshold is the allowed socket power consumption permitted across the voltage rails supplying the socket. Applications with high thread counts, and/or“heavy” threads, can encounter PPT limits that can be alleviated with a raised PPT limit.

            a.Default for Socket AM4 is at least142Won motherboards rated for 105W TDP processors.

            b.Default for Socket AM4 is at least 88W on motherboards rated for 65W TDP processors.

2.Thermal Design Current (“TDC”):The maximum current (amps) that can be delivered by a specific motherboard’s voltage regulator configuration in thermally-constrained scenarios.

            a.Default for Socket AM4 is at least 95Aon motherboards rated for 105W TDP processors.

            b.Default for Socket AM4 is at least 60A on motherboards rated for 65W TDP processors.

3.Electrical Design Current (“EDC”):The maximum current (amps) that can be delivered by a specific motherboard’s voltage regulator configuration in a peak (“spike”) condition for a short period of time.

            a.Default for Socket AM4 is 140Aon motherboards rated for 105W TDP processors.

            b.Default for Socket AM4 is 90A on motherboards rated for 65W TDP processors.

Essentially, AMD’s Precision Boost 2 automatically adjusts clock speeds to stay within the above limits. Setting your system up to use Precision Boost 2 is perfectly safe as the CPU’s guidelines are relatively conservative.

Precision Boost Overdrive

Precision Boost Overdrive or “PBO” works the same as Precision Boost 2. However, instead of using the CPU’s established default limits for PPT, TDC and EDC, it uses those values as defined by the motherboard. When PBO is enabled, the same algorithm is applied, but operates within the limits set by the motherboard’s firmware. Once enabled, it’s just like PB2 in that you can essentially set it and forget it. The processor will adjust its clock speeds up or down as needed. Motherboard VRM implementations, firmware configuration and thermal solutions vary greatly. As a result, PBO results can vary quite a bit. PBO still doesn’t raise the limits of any core beyond the specified boost clock limits. So, if you have a processor like the Ryzen 9 3900X with a maximum boost clock of 4.6GHz, no core will ever go beyond that value.

However, 3rd generation Ryzen CPU’s have the ability to use a maximum boost clock offset which is adjustable in 25MHz increments up to 200MHz. This means that a boost clock of 4.6GHz can now be extended to 4.8GHz under the right conditions. It is a separate feature from PBO specifically, called Auto-OC by AMD. However, it works on conjunction with PBO. The limits still apply as it will not reach those extended frequencies unless it can do so within the established PPT, TDC and EDC limits of the motherboard. Essentially, conditions have to be ideal to allow for the CPU to achieve the desired 4.8GHz boost clock in this scenario. Cooling and environmental conditions come into play with all of that so your mileage may vary. However, compared to PB2, PBO+Offset would be considerably more aggressive and the chances you’ll see those higher boost clocks are much greater. Speaking from personal experience as well as from the testing, PBO works very well to increase performance in lightly threaded applications.

There is data out there from the 1st generation and 2nd generation Ryzen launches showing PB2 and PBO giving greater performance benefits than manual overclocking in some scenarios. Basically, any application that can’t use all the CPU’s cores and threads will potentially be faster using PBO or PB2 than manual overclocking.

Manually Overclocking the Ryzen 9 3900X

Unfortunately, I had no idea what to expect from the CPU in terms of manual overclocking. When you cover these types of launches, you aren’t always told what to expect in terms of overclocking. At least, that’s been my experience. Given the PBO+offset feature and previous Ryzen overclocking experience, I was hoping to at least achieve an all core manual overclock equal to the maximum boost clock, or at least get close to it. As always, overclocking with a new processor and platform always creates a learning curve. However, overclocking with the 3rd generation Ryzen, is similar to the 1st and 2nd generation CPUs in most respects. Mainly, overclocking all cores manually works the same as it did previously. All you really need to do is adjust your load-line calibration and set your CPU voltage. After that, it’s simply a matter of adjusting your CPU voltage until you achieve stability at a given frequency.

However, there are significantly more options for tuning the UEFI BIOS than I’ve seen on previous socket AM4 motherboards. X570 is also somewhat immature, although already worlds ahead of where X370 was at its launch. In any case, I do need to spend more time with this specific motherboard and CPU combination. That is something I’ll be doing in the future as I still need to review the motherboard.

I found that the system could POST at speeds up to 4.6GHz, but at that speed it was unable to reach the Windows desktop. No amount of voltage would change this. I even went as far as 1.55v with no success. All the load-line calibration settings and increasing the SoC voltage didn’t help either. A word of warning, the UEFI BIOS of the MSI MEG X570 GODLIKE warned that PCI-Express 4.0 signaling would be dropped and negotiated to PCIe Gen 3.0 speeds if the SoC voltage went past its default 1.1v value. I continued my testing and found that I could get the system into Windows at 4.5GHz, but it was far from stable. Essentially, I couldn’t actually run any applications that put significant strain on the CPU. Some of the game benchmarks would run, but none of the processor intensive applications would. Attempting to do so would cause the system to randomly reboot on me.

Dropping the clocks down to 4.4GHz @ 1.35-1.4v and beyond bore no fruit either. While I could run many of the benchmarks the system was ultimately unstable. It couldn’t complete any of the major CPU intensive applications. Game benchmarks like Heaven would simply crash to desktop. This is where I feel the CPU’s maximum capability probably lies. Its stable enough to give me some hope that the right combination of settings might work to make it stable. One thing I noticed was that the CPU temperature never went higher than 79c. That’s not exactly cool, but its far from throttling at that temperature. Most of the time the crashes occurred while it still read within the 65c-70c range. This tells me that it isn’t temperature that’s the issue here. It may simply be a setting, or it might actually be past the CPU’s maximum clock speed for all its cores.

At 4.3GHz and 1.35v, I could leave almost everything at its default values and the system was rock solid and ran any test I threw at it without issue. This is the value I settled on for my maximum “all core” overclock. As I said, I feel like manual mode shortchanges you when you can pick up single threaded performance through considerably higher boost clocks using PBO or PBO+Offset. I did try these modes, but I need to spend more time with them. PBO+Offset has no guarantee of granting you the extra clock speed and in my case it never did. However, I saw PBO boost into the 4.5GHz range fairly often in single threaded tasks. However, PBO and PB2 rarely achieved more than 4.2GHz on heavily multi-threaded workloads. In the UEFI, you do have control over the PPT, TDC and EDC values. Ryzen Master gives you access to these as well.

Our testing did show a benefit to the manual overclock in some cases. However, if your buying this primarily for a gaming system, I think the added heat, power consumption and effort probably isn’t worthwhile. This is something I saw back with the 2nd generation Ryzen CPU’s. On my own personal system, I’ve often found PBO to be the way to go, although you do pick up more performance in some tasks using an all core manual overclock. This obviously depends on your usage case.

Dan Dobrowolski
Dan has been writing motherboard reviews for the past 15 years, with the first decade or so writing for [H}ard|OCP. Dan brings his depth of knowledge about motherboards and their components to his reviews here at The FPS Review to help you select the best one for your needs.

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