Zen 2 "best core"

[porina]

In Ryzen master it indicates 4 cores on my 3700X:
Fastest core
2nd fastest core on same CCX
Fastest core of other CCX
2nd fastest core of other CCX

 

The thought occurred, does this impact the speeds the cores turbo to? Let's set a single thread load and see what happens.

 

Remembering CPU-Z has a stress test, I set it to run in a single thread. The version I'm running had different options, and I left it on default 17.01.64. Using Windows Task Manager, I could move that thread to where I want. I used Ryzen Master to monitor the core clock. As SMT was on, there are twice as many CPU threads available as there are cores. I only used the even numbered ones for this test, and didn't check the corresponding odd thread was the same or not.

 

0 4355 4373
2 4366 4355
4 4344 4346 2nd fastest on ccx
6 4380 4380 fastest on ccx
8 4330 4331
10 4392 4390 2nd fastest on ccx
12 4384 4382 fastest core
14 4330 4332

 

I ran this twice, before and after I had lunch so there was some time between. On each occasion I started on thread 0, and move up 2 each time. CPU temp was around 55C during this testing. It is interesting for most cores, the two readings are essentially the same. Only for threads 0 and 2 was there much of a shift. I don't have proof of why this happened. It may be a combination of two mechanisms. One, that the CPU is cooler at the start of the test than at the end. Secondly, as I was just starting this test for the first time, there may have been other background activity slowing it down a little. For the 2nd run, I did allow it to run for much longer, and the values shown seem stable, even returning to threads 0 and 2 after completing the others.

 

The Ryzen Master "fastest core" wasn't actually fastest here, with the 2nd fastest on same CCX slightly ahead of it. On the other CCX, indicated fastest was indeed fastest, but the indicated 2nd fastest was slowest.

 

Maybe it is something to do with the workload? Let's put something heavier on it. Prime95 128k FFT, single in-place load.

 

0 4287 4300
2 4306 4287
4 4235 4218 2nd fastest on ccx
6 4275 4253 fastest on ccx
8 4274 4260
10 4303 4304 2nd fastest on ccx
12 4262 4261 fastest core
14 4225 4230

 

CPU temps were hotter, starting around 70 going up to 72C by the end. On the first pass I went from thread 0 to 14, and on 2nd pass I went from thread 14 back down to 0.

 

I think thermal throttling is making an impact here with a bit more variation between the cores on each pass.

 

Like before, the fastest core remained slightly behind the 2nd fastest core on same CCX. On the other CCX, the indicated two fastest cores were actually slowest. While there is some consistency, it isn't exact between the two workloads.

 

Still, I'd like to offer these observations as a starting point in case it might be useful for something. My motivation was to see how the system handles these cores.

 

Key hardware/software
CPU 3700X
Cooler: 240mm AIO
AGESA 1.0.0.3ABBA
Ram: 3600 dual channel
PBO enabled
Win10 1903, with AMD chipset driver and Ryzen Master updated to latest shortly before test

[TheNaitsyrk]

9 minutes ago, porina said:

SNIP

Thanks for sharing. It's an interesting point of view. 

I remember having 1800X and 2700X and I remember seeing those "favoured" cores, but I never could be bothered to test if they are actually best.