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AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

arstechnica.com

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Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#101

Post by acomjean »

MegaDeKay wrote: post #19
pwg wrote: post #10

Earlier quoted context omitted.

In my case it began with 16K (yes, 16 1024 bytes) and 90K (yes, 90 1024 bytes) 5.25" floppy disks (although the floppies were a few months after the computer). Eventually upgraded to 48K RAM and 180K double density floppy disks. The computer: Atari 800.

I'll see your Atari 800 and raise you my Atari 2600 with its whopping 128 bytes of RAM. Bytes with a B. I can kinda sorta call it a computer because you could buy a BASIC cartridge for it (I didn't and stand by that decision - it was pretty bad).

I thought the timex Sinclair 1000 win 2 Kbytes of ram was bad.

The membrane keyboard wasn’t great (the lack of a space bar was a wierd choice) but it did work. We had programs on casette and did get the 16Kbyte memory expansion.

https://en.wikipedia.org/wiki/Timex_Sinclair_1000

I didn’t realize the Atari 2600 had basic, always thought of it as a game console.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#103

Post by justincormack »

monster_truck wrote: post #93
YoumuChan wrote: post #72

Earlier quoted context omitted.

But consumer product does not support SDCI (only Epyc Turin supports it), so it does not benefit too much if an accelerator is involved.

It's also useful to point out that the use cases and workloads where SDCI are most beneficial are far, far beyond the scope of what anyone will have installed in a Zen rig. Dual 100G networking cards? The cost of both of those damn near buys all of a 9950X3D2 setup.

no, dual 100Gb are not that expensive any more, eg https://www.scan.co.uk/products/2-port-intel-e810-cqda2blk-d... UK retail for gbp349.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#104

Post by undersuit »

pwr22 wrote: post #99

I'm interested to know if the L3 cache all behaves as a single pool for any core on either CCD, whether there's a penalty in access time depending on locality or whether they are just entirely localised.

AMD didn't have to introduce a special driver for the Ryzen 9 5950x to keep threads resident to the "gaming" CCD. There was only a small difference between the 5950x and the non-X3d Ryzen 7 5800x in workloads that didn't use more than 8 cores unlike the observed slowdowns in the Ryzen 9s 7950X3D and 7900X3D when they were released compared to the Ryzen 7 7800X3D .

When the L3 sizes are different across CCDs the special AMD driver is needed to keep threads pinned to the larger L3 CCD and prevent them from being placed on the small L3 CCD where their memory requests can exploit the other CCD's L3 as an L4. The AMD driver reduces CCD to CCD data requests by keeping programs contained in one CCD.

With equal L3 caches when a process spills onto the second CCD it will still use the first's L3 cache as "L4" but it no longer has to evict that data at the same rate as the lopsided models. Additionally the first CCD can use the second CCD's L3 in kind reducing the number of requests that need to go to main memory.

The same sized L3s reduce contention to the IO die and the larger sized L3s reduce memory contention, it's a win-win.

https://www.phoronix.com/review/amd-3d-vcache-optimizer-9950...

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#105

Post by aetimmes »

tarangsutariya wrote: post #89
magicalhippo wrote: post #25

Probably fun for those who already bought DDR5 memory... still kicking myself for not just pulling the trigger on that 128GB dual stick kit I looked at for $600 back in September. Now it's listed at $4k... Meanwhile I hope my AM4 will chug along a few more years.

Wonder how much sales amd and intel are losing because of tight DDR5 supply

None. Every component is seeing huge demand.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#106

Post by throwup238 »

Aurornis wrote: post #49
magicalhippo wrote: post #47

Earlier quoted context omitted.

No such bundle deals where I am. Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k. Cheapest 64GB kit is $930. The kit I was oh-so-close to buying was two 6400 64GB sticks. Not gonna buy now, not that desperate. I have a spare AM4 board, DDR4 memory and heck even CPU, I'll ride this one out. Likely skip AM5 entirely if something doesn't drastically change.

> Absolute cheapest DDR5 128GB kit around is 2 sticks of 5600 64GB for $2k. That's not far from the bundle deal above, once you subtract the $700 CPU. If you really need 128GB the 5600 kit is fine. Having 208MB of total cache on the CPU means the real world difference between a 5600 kit and a slightly faster kit is negligible in most use cases. If you don't need to upgrade then clearly don't force an upgrade right no…

> a slightly faster kit is negligible in most use cases

Does that “most use cases” caveat really apply to someone buying 128G of RAM? If I’m buying that much, it means I’m actually going to put it through its paces, unless it’s just there for huge reserved guest VM overhead.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#107

Post by HauntingPin »

2001zhaozhao wrote: post #69
sspiff wrote: post #62

Earlier quoted context omitted.

I bought 192GB (4x 48GB) of DDR5-6400 for 299 euro in September but returned it because I couldn't get 4 DIMMS to run at decent speeds in the system. 6 or so weeks after I returned it the kit was listed at 1499.

Yeah the only way to run 4 sticks of DDR5 decently is with Intel. It's a bit of a shame that you can't cram enough RAM to run big models. The most I could get running on 10GB VRAM + 96GB RAM was a REAP'd + quantized version of MiniMax-M2.5

I had the same issue with Intel. It's not guaranteed there either.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#108

Post by phire »

pwr22 wrote: post #99

I'm interested to know if the L3 cache all behaves as a single pool for any core on either CCD, whether there's a penalty in access time depending on locality or whether they are just entirely localised.

The short answer is that L3 is local to each CCD.

And that answer is good enough for most workloads. You should stop reading now.

_______________________

The complex answer is that there is some ability one CCD to pull cachelines from the other CCD. But I've never been able to find a solid answer for the limitations on this. I know it can pull a dirty cache line from the L1/L2 of another CCDs (this is the core-to-core latency test you often see in benchmarks, and there is an obvious cross-die latency hit).

But I'm not sure it can pull a clean cacheline from another CCD at all, or if those just get redirected to main memory (as the latency to main memory isn't that much higher than between CCDs). And even if it can pull a clean cacheline, I'm not sure it can pull them from another CCD's L3 (which is an eviction cache, so only holds clean cachelines).

The only way for a cacheline to get into a CCD's L3 is to be evicted from an L2 on that core, so if a dataset is active across both CCDs, it will end up duplicated across both L3s. Cachelines evicted from one L3 do NOT end up in another L3, so an idle CCD can't act as a pseudo L4.

I haven't seen anyone make a benchmark which would show the effect, if it exists.

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#109

Post by makapuf »

acomjean wrote: post #101
MegaDeKay wrote: post #19

Earlier quoted context omitted.

I'll see your Atari 800 and raise you my Atari 2600 with its whopping 128 bytes of RAM. Bytes with a B. I can kinda sorta call it a computer because you could buy a BASIC cartridge for it (I didn't and stand by that decision - it was pretty bad).

I thought the timex Sinclair 1000 win 2 Kbytes of ram was bad. The membrane keyboard wasn’t great (the lack of a space bar was a wierd choice) but it did work. We had programs on casette and did get the 16Kbyte memory expansion. https://en.wikipedia.org/wiki/Timex_Sinclair_1000 I didn’t realize the Atari 2600 had basic, always thought of it as a game console.

You can buy this bad boy [attiny11] with no ram, only registers.

https://ww1.microchip.com/downloads/en/DeviceDoc/1006S.pdf

Re: AMD's Ryzen 9 9950X3D2 Dual Edition crams 208MB of cache into a single chip

#110

Post by Numerlor »

monster_truck wrote: post #91
Aurornis wrote: post #40

Earlier quoted context omitted.

> The extra cache doesn't do a damn thing (maybe +2%) It depends on the task. For some memory-bound tasks the extra cache is very helpful. For CFD and other simulation workloads the benefits are huge. For other tasks it doesn't help at all. If someone wants a simple gaming CPU or general purpose CPU they don't need to spend the money for this. They don't need the 16-core CPU at all. The 9850X3D is a better buy for mo…

It really doesn't. In virtually every case the work is being completed faster than the cache can grow to that size. What little gains are being realized are from not having to wait for cores with access to the cache to become available.

There are some very specific workloads (say simple object detection) that fit into cache and have crazy performance where the value of the cpu will be unbeatable, as the alternative is one of the cache epycs, everywhere else it'll only be small improvement if the software is not purpose made for it
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