Just 19-20 years ago, extra L3 cache or any L3 cache used to help in almost all workloads

[Wolverine2349]

Intel's New Weapon: Pentium 4 Prescott

Maxon Computer Cinema 4D XL 8.503

www.tomshardware.com

I remember in the Fall 2003 reading about Intel's Pentium 4 Socket 478 Extreme Edition and it had L3 cache of 2MB for like $1000 and I was intrigued but did not buy it.

The regulars Pentium 4 Northwoods had no L3 cache.

Now we have the Ryzen 7800X3D vs 7700X and 5800X vs 5800X3D. Difference is there is 96MB L3 cache vs only 32MB.

Today yet almost all workloads except gaming do better with the lower cache amount.

Yet back then, almost every workload including games did better with Pentium 4 Northwood Extreme edition that had 2MB L3 cache as opposed to the no L3 cache Pentium 4 Northwoods.

Why is that. Is it all about lower clocks on extra cache Ryzen counterparts where as Pentium 4 EE 2MB L3 cache had equal or higher clocks.

Or has more changed in 20 years where extra L3 cache even at same clock speeds can be a disadvantage on some CPUs today as opposed to the early 2000s?

 

[Wolverine2349]

it’s all about correctly sizing the cache for the workload.

SO basically is the extra cache kind of a gimmick in that it onky benefits games where as 32MB L3 is optimized proper cache size for whole set of workloads?

Was basically the extra 64MB stacked on top kind of a test phase and not optimized except for gaming workloads. But if AMD tried to design CPU with extra cache and optimize it it would be better in all workloads.

I mean did Intel back then with the Pentium 4 Extreme Edition optimize L3 cache to benefit all workloads and it was nit just a gimmick add on for only specific workload types?

 

[Wolverine2349]

I don’t think games use that much random IO, they use some, but game engines are very organized batch possessors. Everything is in large tightly packed and aligned buffers. They also use a lot of SIMD/AVX which must be tightly packed and aligned to work. Feeding these buffers to the CPU is very cache friendly as it easy to tell what is needed next. Random IO is NOT cache friendly no matter how much L3 you have.

Does more L3 cache often make random IO worse even if clock speed is the same?

 

[Wolverine2349]

If you look closer its not the extra cache that causes a performance hit outside of gaming. Its the drawbacks that come with that cache such as lower clock speed and thermal headroom that cause the performance hit not extra cache capacity.

Oh ok I see. So basically at same clock speeds, extra cache should make no difference or actually help in all other workloads?

Its just that thermal headroom is much weaker so clock speeds are more volatile and can go lower and even much lower causing performance loss?