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Old 2019-09-20, 10:20   #11
M344587487's Avatar
"Composite as Heck"
Oct 2017

89310 Posts

Originally Posted by mackerel View Post
Anyway, it has been some time since I ran those early tests. I currently have both a 3600 and 3700X so I can repeat the testing later. Bios has improved a lot, particularly for ram compatibility since those early days. I can run 3600 ram in those systems, as well as trying something "slower" like 3000 or 3200. There is also something I've not tested, I've heard in other applications there can be benefit from running IF at higher speed than keeping it sync'd with ram clocks, so that would be an interesting test also.
It's my understanding that decoupling Fclk from RAM mainly has some impact on latency as there's extra complication keeping things in sync. Fclk can get to around 1900 although not every chip can get there, some can get a bit higher. These tests would yield some nice comparison points if you have the patience:
  • 3200 in sync at 1600 Fclk, baseline
  • 3600 in sync at 1800 Fclk, baseline
  • 3200 decoupled at 1800 Fclk, comparable to 3600 baseline
  • 3600 decoupled at 1900 Fclk or whatever Fclk you can get
  • 3200 decoupled at 1900 Fclk or whatever Fclk you can get

My hypothesis is that decoupling will greatly help 3200 DDR4 but be a wash for 3600 DDR4. Increasing Fclk may also disproportionately help tests that stay mainly in cache so testing at least three FFTs per setup would be nice for comparison (fully in cache, wavefront which straddles cache and RAM, 100M which is mainly in RAM).
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