Does the extra cache of the new 5800X3D increase crunching?

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ProDigit

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Message 108296 - Posted: 1 Jun 2022, 3:42:57 UTC

AMD Ryzen 7 5800X3D, how much does it speed up data crunching on a variety of cpu project?
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Profile Dave
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Message 108297 - Posted: 1 Jun 2022, 5:18:05 UTC

Depends very much on the type of work unit. AFR tasks from WCG and N216 tasks from CPDN both slow down appreciably on my Ryzen due to lack of level3 cache if I run on more than 5 out of 8 real cores. Other projects like SiDock, I can go up to using at least four virtual cores and 8 real ones with no noticeable slowdown. Other CPDN tasks slow down if I use virtual cores but no slow down before that. OpenIFS tasks in testing I can't be sure about because with only 32GB RAM they start using swap heavily before I I get a chance to see if cache is a problem.
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ProDigit

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Message 108342 - Posted: 8 Jun 2022, 8:27:57 UTC
Last modified: 8 Jun 2022, 8:33:29 UTC

I found a semi-suitable answer on the Folding forums.
At least for their client, a 5800x vs 5800X3D, are nearly identical in performance.
The X3D has about like 1% higher performance, despite it having a few hundred megahertz lower CPU speeds.
So the performance drop of the lower CPU frequency of the X3D, gets compensated in performance by the extra 3D RAM.
Quite literally, for folding the 5800x folds at 320k PPD, the 5800X3D folds at 322k PPD.

In most cases, it makes more sense buying a 5900x or 5950x, or even a 3900x, and disable HT, and you'll be running WUs much more efficient and fast.
Not only do you double the L-Cache per thread on the 3900/5900 series CPUs (as you cut the threads down by 50%), but also, the 5900x/5950x has 16 full cores, while the 5800x3D only has 8 full cores, 16 threads.
They say on average a dual threaded core roughly increases performance of a single core by just 33%.

The lack of L-Cache doesn't really seem a problem for most projects.
Disabling HT/SMT will allow the CPU to run cooler, and at higher frequencies, but does come with a drop in performance.
In this, the CPU follows the pattern of the GPU, where more cores generally is better, even if it's lacking L-Cache; and the CPU loses some cycles filling up that L-Cache between runs.
This appears to be the case all the way up to about 20 threads, where both L-Cache and believe it or not, the RAM speed, will become the limiting factor on crunching data.

Some tests have shown that the performance on a 3950x (16C/32T) seems to level out at around 20-22 threads.
Any more, and the CPU doesn't perform any faster (probably could also be power throttled).
However, once you hit closer to 28-30 threads, the CPU actually starts losing performance over less threads, to the point where 32 threads are no faster than 26 to 28 threads!
And that's something quite strange!
In the case of the 3950x, it may be better to test between disable or enable SMT, and not sure if that performance problem persists on the 5950x.

PPD wise, a 3900x gets 380kPPD, while the 5800X3D gets 322k PPD, or a PPD difference of 29.5%.

Considering that you can now get a much newer, faster 5900x for much cheaper in price than an older 3900x right now ($~380 vs $550), or the 5950x (16C/32T)for the price of a 3900x (12C24T), it makes only sense to go for a 5900x or 5950X if you want to do any CPU intensive computations.
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Message 108346 - Posted: 8 Jun 2022, 10:00:17 UTC

.. and just as I write this, news from ryzen 7000 cpus (Zen4) comes out...

Perhaps a 7950x or 7900x might be the best buy.
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Message boards : Questions and problems : Does the extra cache of the new 5800X3D increase crunching?

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