Ryzen 5 3600 FCLK OC confusion

[itsakjt]

Hello everyone, this is regarding overclocking on my primary system as on specs. As far as I read everywhere, it is recommended that the MCLK and FCLK should be in the 1:1 ratio for best performance. However, I tried playing with the FCLK and have set it at 1900 MHz at stock SOC voltage (anything above that results in failed POST) and for some reason, I have seen a bump in performance across benchmarks especially memory bandwidth intensive benchmarks (verified with AIDA 64). It is also worth noting that my RAMs are quite old from 2015, dual ranked with stock XMP at 2666 MHz. I have been able to overclock it 3266 MHz rock stable at 1.36V.

With the FCLK set to 1900 MHz, the latency creeps up by about 4 ns but at the same time, the memory write speed in AIDA also bumps up to 30400 MB/s from 25599 MB/s. The CPU Photoworxx benchmark which relies on memory bandwidth is also about 2500 points higher.

So my question is why is it that everyone recommends putting the FCLK and MCLK as 1:1? I am confused because my experience suggests otherwise. Any inputs are appreciated.

 

[GerKNG]

because your scenario is the exact opposite.

normally people run ram higher than the max stable FCLK and then it gets cut in half.
and faster RAM with a slower FCLK that is not 1:1 skips clocks and the overall performs falls off a cliff.

 

[itsakjt]

because your scenario is the exact opposite.

normally people run ram higher than the max stable FCLK and then it gets cut in half.
and faster RAM with a slower FCLK that is not 1:1 skips clocks and the overall performs falls off a cliff.

I did not get you. I have seen people running 3200 MHz RAMs with 1600 MHz FCLK or just left it at auto (which essentially sets itself to half of whatever the effective DDR frequency is or equal to the value of MCLK). Even AMD Ryzen Master does not allow the FCLK to be set higher than the MCLK. But since the BIOS has the flexibility, I tried it and it has been a win.
While it's true that increasing the MCLK (if RAMs are capable) and setting the highest possible FCLK is guaranteed to increase performance, the other way round does not have much exposure and I am just wondering why since it has done wonders for my exact system at least.
I did try setting 1900 MHz FCLK as well on my friend's Ryzen 5 3600 based system with an MSI B450 motherboard and 3200 MHz TridentZ and he has got similar performance gains as well.

 

[Nomad8459]

Running FCLK as high as possible with lower memory clocks does boost performance indeed, however you are better at 1:1 ideally at 1:1 you get the best Latency AND the best performance for example i have 3600mhz ddr4 DIMMS, i have overclocked these to 3800Mhz and set the FCLK and MCLK to 1900mhz - about the highest you can expect on ryzen 3000 series, i believe some Ryzen 5000 series CPUs will do 2000Mhz FCLK however.

Buildzoid on Youtube has a good video comparing the effects of the FCLK - as has been said before running higher than FCLK memory is where it stumbles say 1900Mhz FCLK with 4000Mhz ram, or say you run 4200Mhz RAM and the FCLK halves itself again to 1050 FCLK and adds Latency, also memory timings play a big part, tightening your timings will help with your latency