Zen 2 comparison of monolithic 4650G versus chiplet 3500X

Ryzen raise on desktop is really well benchmarked and tested. We know how it scales with memory and so on. But what about mobile parts? How much do the loose stuck at 3200CL22 JEDEC RAM? Are there any other less obvious compromises that affect performance? Lets take a look.

This article is a comparison of mobile APU design (Ryzen 4650G) versus desktop chiplet Ryzen 3500X. Even though 4650G should perform bit better than 3500X there is an unexpected performance drop in relatively lightweight gaming with a dedicated GPU - I'll go over various aspect of the system to see what's causing this.

If you want a quick overview on how it performs you can check my World of Warcraft benchmarks as well.

Intro

When Intel launched Tiger Lake they did use LPDDR4X advantage to beat Ryzen 4800U using standard 3200CL22 SO-DIMM. Aside of iGPU performance it affected some synthetic benchmarks focused around memory.

15W U-series Zen 2 chips like the 4800U downloclock RAM to 2666MHz when they encounter a CPU-only workload to favor lower latencies. Full RAM speed is used when heavy GPU workload is detected. Tiger Lake doesn't do that so with LPDDR4X it offers much higher memory throughput and high gains in some synthetic benchmarks. Such benchmarks don't mimic real world usage really well but can showcase such less known characteristics of a mobile APU that can come back in some scenarios…

Such less known features, behaviors of mobile parts can cause confusion. PC builders know they can’t really got beyond 2000 MHz for Infinity Fabric on a Zen 2 or Zen 3 CPU but with Zen 2 APU you can go way beyond that which could be utilized for even better performance.

We also know that Zen 3 is really strong in gaming, but if you move to laptops the results can be quite different:

5800H vs 10875H in gaming on a laptop

5800H vs 10875H in gaming on a laptop

A Zen 3 latest mobile CPU is bit slower than old 14nm Intel CPU? How come? It’s not a direct CPU to CPU comparison due to different laptops, yet such dark corners of benchmarking and analysis of the mobile parts still persist.

Test setup and initial comparison

I've decided to compare desktop Ryzen 3500X Matisse CPU with Ryzen 4650G - a Renoir Zen2 APU. How they behave in CPU workloads (taking into account their core/clock differences) and how they will perform in gaming with a dGPU? Can you use an APU right now for a solid PC that later would get only dGPU without the need to upgrade the CPU?

I've used Gigabyte B450M DS3H and Asrock A520M-HDV motherboards with multiple kits of memory, all described in my DIMM vs SO-DIMM benchmarks.

Ryzen 3500X Matisse Ryzen 4650G Renoir
Core configuration 6C/6T 6C/12T
Base/Boost Clock 3.6 GHz / 4.1 GHz 3.7 GHz / 4.2 GHz
L1 / L2 / L3 cache 384KB / 3MB / 32MB 384KB / 3MB / 8MB
TDP 65W 65W
Floorplan / die shot wikichip.org guru3d.com
dGPU GTX 1070

3500X has more L3 cache but 100MHz lower frequency and doesn't have SMT. In synthetic benchmarks that use SMT this should show up:

Cinebench R20 Single
Cinebench R20 Multi

Everything seems in order. Slightly higher clocked 4650G wins a bit in single core and more in multi due SMT. 8/16 4800U tops the multi-core Cinebench run even while being low power chip.

If we go to some simple CPU benchmarks like say Geekbench 5 the trend will continue:

3500X vs 4650G Geekbench 5 comparison
3500X vs 4650G Geekbench 5 multi comparison

In the single core clock difference is quite small and the load isn't long lasting so both CPUs end up nearly equal. In multi-core 6/12 wins with 6/6, especially if you are working with some archives and alike plus 4650G has lower latencies which should boost some Geekbench scores.

Also as you can see single channel of 1x8GB RAM is much slower than dual-channel configurations. 4-stick configuration for bank weaving (all sticks are single rank) doesn't do much for Zen 2 (for Zen 3 the effect of bank or rank weaving is bigger).

Ok, lets move to some gaming benchmarks, like say 3DMark benchmarks?

3500X vs 4650G Night Raid

So it looks like 4650G is slightly better than 3500X aside of single-channel and low-end SODIMM configuration? But wait - 3DMark scores consist of GPU and CPU benchmarks:

3500X vs 4650G Night Raid CPU

6/12 low latency wins with 6/6 higher latency which shouldn't be a surprise. But if CPU score is so high, what's the GPU scores like?

3500X vs 4650G Night Raid GPU score

Welcome to our investigation. Why does 4650G has a lower GPU score than 3500X? Is it because of PCIe lanes differences? And why does it scale with memory so much?

Unigine Superposition
Unigine Valley

And if we look at framerate in World of Warcraft with the help of MSI Afterburner we get this:

World of Warcraft Stonard
4650G with GTX 1070

Both CPUs reach their target frequencies, temperatures are well below high and all seems to be working fine.

Is it the PCIe lanes difference?

3500X runs the x16 slot at x16 PCIe 3.0. The 4650G should offer x16 for the GPU but if the motherboard uses any extra PCIe lanes for I/O it will run the same x16 slot at x8 PCIe 3.0 speed. If you run 3DMark PCIe bandwidth benchmarks it will be super clear:

3DMark PCIe bandwidth benchmark

3DMark PCIe bandwidth benchmark

3DMark API overhead benchmark

3DMark API overhead benchmark

3500X has double the PCIe bandwidth which also allows it to spam more draw calls for DX12 and Vulkan which are parallelized enough to hit the PCIe bandwidth limit in a synthetic benchmark. DX11 is mostly single threaded so the 4650G with stronger single core clocks wins by a bit.

If I reduce the PCIe version to 2.0 for 3500X (x16 2.0 is equal to x8 3.0) we get this:

3DMark PCIe bandwidth benchmark

3DMark PCIe bandwidth benchmark

3DMark API overhead benchmark

3DMark API overhead benchmark

So we have a tie on PCIe bandwidth as expected. 3500X still wins in DX12 by a very small margin, Vulkan goes crazy in favor of 4650G and for DX11 it has a ~10% lead.

Does it affect games? - no, not really:

3500X x16 PCIe 3.0 3500X x16 PCIe 2.0 4650G x8 PCIe 3.0
Superposition 25492 25677 21400
Unigine Valley 7349 7294 5986
Night Raid GPU score 77 166 76 977 74 488

Shouldn't Renoir have 16 + 4 + 4 PCIe configuration?

4650G should offer x4 PCIe for NVMe SSD, second x4 for chipset and then x16 for the GPU. The problem will be when the motherboard uses some extra lanes for additional SATA controller or other I/O. The Renoir will be in a disadvantage and the lanes for the GPU will drop to x8 - this is motherboard dependent... Matisse has same amount of lanes but PCIe 4.0 while Renoir 3.0. Lack of x16 to the GPU could be also to some werid config in the BIOS as Gigabyte B450M DS3H doesn't explicitly use extra PCIe lanes for anything special.

System topology on the Gigabyte B450M DS3H listing multiple PCI devices

System topology on the Gigabyte B450M DS3H listing multiple PCI devices

SoC design

Desktop Matisse and mobile Renoir use different designs. 4650G even as a desktop CPU is based on a mobile monolithic design. 3500X consists of I/O die (GlobalFoundries 12nm) and a Core Complex Die (TSMC 7nm) that consists of up to two CPU Complexes. Each complex can have up to 4 cores, 8 per CCD. Both complexes are connected via interconnect and as a CCD they are connected to the I/O die than then handles RAM and other peripherals.

Renoir is a single chip consisting of one CCD (so up to 8 cores) with Core complexes similar to Matisse but with only 4MB of L3 cache instead of 16MB. As there is no separate I/O die, no additional CCD and distances are much shorter and all on-die the latency of internal communication is much lower. Also the memory controller supports much higher frequencies under 1:1 ratio with Infinity Fabric clock - meaning you can use an extreme kit of DDR4 memory with APU but not necessarily with the Zen 2 or Zen 3 chiplet based CPUs.

Latency was one key aspect in which Intel CPUs excelled which allowed them to retain the king of gaming crown, especially in latency sensitive games. With Zen 3 it's improved but with monolithic APU designs the differences should be even smaller if not lower on some extreme kits of memory.

If we look at 3DMark Time Spy and Firestrike results comparisons we can see how 4650G annihilates 3500X in CPU based benchmarks while still loosing by a bit in GPU ones:

3DMark Time Spy comparison

3DMark Time Spy comparison

3DMark Firestrike comparison

3DMark Firestrike comparison

This is lower latency of internal communication (and sometimes SMT) more so than +100MHz to the clocks.

Monolithic vs chiplet memory controller differences?

If the monolithic design has improved latencies and wider Infinity Fabric link we should see that in Aida64 benchmarks (A520 3600CL16):

Memory comparison
Latency
L1 cache
L2 cache
L3 cache

As we can see 4650G has bit lower latencies and higher cache throughput. The L3 results are bit weird but if we look at some lower RAM frequencies (B450) we get more consistent results like look like so:

L3 cache
Latency

Renoir can dynamically manage the IF link, throttling it if needed so that's why some results from higher frequency memory may be atypical on some systems.

Are we trolled by pro features?

As standard APUs (4600G, 4700G) are not available to end users but 4650G and 4750G are we get pro management and security features that big companies, governments or Arasaka wants. One of such features is TSME (which is not TSMC alter ego). TSME is physical memory encryption and when enabled it will impact memory related performance. For normal PCs this should be disabled. On the Gigabyte B450M DS3H I had to look deep inside menus to find it and disable it - it even didn't had a tooltip string.

For PRO APUs you should disable memory encryption - TSME

For PRO APUs you should disable memory encryption - TSME

After disabling TSME I rerun some of the benchmarks:

  • Superposition: 22 295 (from 21 400; 3500X at 25 492)
  • Unigine Valley: 6071 (from 5986; 3500X at 7349)
  • Night Raid: 39 455 (from 38 945; 3500X at 37 822)
  • Night Raid GPU: 72 635 (from 71 120; 3500X at 77 101)
  • World of Warcraft (Stonard): 230 FPS (from 229,3 FPS; 3500X at 280,4 FPS)
  • PCMark 10: 6036 (from 5851)
  • Memory latency: 65,3 ns (from 72,1 ns; 3200 16-15-15-35; 3500X at 75,8 ns)

There is some improvement, especially on CPU compute side, but it's nowhere near of 3500X in lightweight gaming performance.

Is it a Windows problem?

Using Ubuntu 21.04 and Phoronix benchmarks I run a set of various gaming and compute/memory related benchmarks. Here are some of the compute ones:

Linux compute benchmarks

As expected 4650G is better in those scenarios. When we switch to gaming we get this:

Linux gaming benchmarks

We get the same pattern - in gaming with dGPU 3500X wins. Also SMT is not the cause of the problem - when disabled in the BIOS it doesn't improve the results.

What are our other options?

Right now I don't know what can be causing this performance disparity. Any ideas? Is it just because 4650G has less Game Cache a.k.a. L3 cache? ;)

How high can you go with RAM on Renoir?

guru3d.com went up to 4533CL16 1:1 in their benchmarks on a premium motherboard so you can check that out - for iGPU, dGPU and CPU compute performance.

Ryzen APUs in pro and non-pro variants are available in pre-build nettops and small PCs. Most of the small ones will use SO-DIMM memory sticks limiting you to pretty much 3200CL22. Note that better SO-DIMM kits you may find use 1.35V and given device is likely not compatible with 1.35V SO-DIMMs – so if you got one check it manual and specs for this before you buy such RAM sticks.

If you are building an APU system to later on add a dGPU you can use a good motherboard with a more premium set of memory to push most of the APU in both configurations. Note that when you stress the memory controller with higher frequency it will generate more heat so to not loose on CPU clocks you will have to cool the APU really well.

Where to get an AMD APU?

Zen 3 APUs have been launched for OEMs so pre-build systems should show up soon from the time of writing this article. Zen 2 APUs are available more or less. Non-pro 4600G or 4700G are only in pre-build systems - small nettops or PCs. Pro variants are in bit more expensive pre-builds but also some stores order trays of those CPUs and sell them to end users. Check your local stores for 4650G. The 4750G is an 8/16 part with Vega 8 instead of Vega 7 but the price is close to double of 4650G so I would say it’s not the best value right now. Aliexpress offers them as well while some also got them locally from Amazon.

Summary

Right now when dGPU, even the placeholder ones are hard to get in sane prices an APU PC intended for dGPU upgrade later on could be a really good and handy build.

There is some difference in light gaming benchmarks but the difference isn't large and for more complex games it may be completely overshadowed by the better CPU performance or just GPU bottleneck when running heavier games.

If I get any tips or ideas what could cause this performance disparity I'll update the article and add corresponding benchmarks.

RkBlog

Hardware benchmarks and reviews, 3 May 2021, Piotr Maliński

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