New comment by adfghopmnoi in "How did AMD Ryzen get 50% faster in two years?"

adfghopmnoi — Wed, 23 Sep 2026 01:30:28 +0000

When we say a design "scales", that means that increasing the size of the workload does not incur a lot of overhead. If contention between shared resources meant that the design was not able to achieve an ~8x speedup when run with eight parallel threads, that would mean the design was not scalable. But we did in fact see a roughly 8x speedup with eight threads, so the design scaled just fine. The problem with the design was that each core was individually crummy, so even eight cores running in parallel had lackluster performance.

The myth that each two-core module functioned more like one core with hyperthreading would suggest that these CPUs would have much higher per-core performance when lightly loaded than when fully loaded. That is not what happened. Each core was crummy even when lightly loaded, but under full load you would have eight crummy cores, which would beat four Intel cores on a lot of workloads.

The only time contention was a serious problem was with workloads that were dominated by floating point, which were relatively rare.

New comment by adfghopmnoi in "How did AMD Ryzen get 50% faster in two years?"

adfghopmnoi — Tue, 22 Sep 2026 23:11:00 +0000

>Instead of discrete, fully independent cores, AMD grouped processing units into "Modules" where each module contained two integer execution units, but they had to share critical resources like one FPU, the instruction fetch/decode pipeline, and the L2 cache so when both "cores" inside a module were heavily taxed especially with math or physics-heavy calculations (like in videogames), they choked fighting over shared hardware.

They did just fine in parallel workloads, so I think this is not accurate. The design scaled just fine. The problem was that each core was weak.

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New comment by adfghopmnoi in "How did AMD Ryzen get 50% faster in two years?"

New comment by adfghopmnoi in "How did AMD Ryzen get 50% faster in two years?"