Design changes in Zen 3 (CPU/core/chiplet only)

[moinmoin]

It's a little less than 2 years since the thread on design changes in Zen 2. It's unfortunate that even a month before the public launch of the first Zen 3 chips we still don't get any meaty information, but with the event we at least got some rough outlines which areas were changed and what their impact is. I hope AMD will fill in the interested public come time.

The 19% IPC improvement broken down into the different areas:

Doc used his pixel counting skill to come up with these numbers:

• +2.7% Cache Prefetching
• +3.3% Execution Engine
• +1.3% Branch Predictor
• +2.7% Micro-op Cache
• +4.6% Front End
• +4.6% Load/Store

The first and essentially only Zen 3 leak, unified L3 cache per CCD, was confirmed:

• Advanced Load/Store Performance and Flexibility
• Wider Issue in Float and Int Engines
• "Zero Bubble" Branch Prediction

More technical details to come, hopefully soon.

+2.7% Cache Prefetching

+3.3% Execution Engine

• "most likely an additional int unit and fp unit, taking it to 5x INT, 3x AGU, 3x FP" via #3

+1.3% Branch Predictor

+2.7% Micro-op Cache

• Paper: Improving the Utilization of Micro-operation Caches in x86 Processors via #5

+4.6% Front End

+4.6% Load/Store

• higher Load/Store rate (Zen was 32B/cycle Load and 16B/cycle before while Intel Skylake featured double each) via #9

 

[uzzi38]

Thanks @DisEnchantment.

We finally have some die porn now:


For comparison, the cores from Zen 1 and Zen 2:

Notable is that with Zen 2 the aspect ratio of the area didn't change, while with Zen 3 it did. (Also to me the debug/wafer test area seems huge, but that's uncore stuff of the CCD so off topic here.)

Somebody willing to do some pixel counting comparing the core sizes?

Zen 3 core size in area looks to be 3.2mm^2 without L2, 4mm^2 with L2. Both up 0.4mm^2 vs Zen 2 cores, so unsurprisingly L2 size has remained tthe same

 

[moinmoin]

Zen 3 core size in area looks to be 3.2mm^2 without L2, 4mm^2 with L2. Both up 0.4mm^2 vs Zen 2 cores, so unsurprisingly L2 size has remained tthe same

Thanks! So the core size without L2$ increased by a little under 15%, sounds good. Pretty much in line with much of the IPC increase (and very effective with SPECint2006).

 

[moinmoin]

Above comparison in a picture:

Zen2 vs Zen3 core, the latter is 15% bigger:



The FPU (1/3 of the picture to the left) seems to be waaay more tightly packed with logic.

 

[CakeMonster]

Do you think there could be any difference in the actual physical transistors? Or does the same process mean its identical? I'm referring to the very interesting video Der8auer did comparing Intel's 14nm+++ and Zen2 with actual microscope images.