Monday, November 27th 2023

AMD 3D V-Cache RAM Disk Delivers Over 182 GB/s and 175 GB/s Read and Write Speeds

AMD's 3D V-Cache technology utilizes blocks of SRAM stacked on top of the CPU logic die, where CPU cores reside, and allows the processor to access massive pools of cache for applications. However, using this extra level 3 (L3) cache as a RAM disk appears possible, where the L3 SRAM behaves similarly to a storage drive. A big disclaimer here is that this is only possible by exposing the L3 to the CrystalDiskMark benchmark, and no real-world applications can do it in a way that CrystalDiskMark. According to X/Twitter user Nemez (@GPUsAreMagic), the steps to replicate this procedure are: Obtaining an AMD Ryzen CPU with 3D V-Cache, installing OSFMount and creating a FAT32 formatted RAM disk, and running CrystalDiskMark, with values set to values to SEQ 256 KB, Queue Depth 1, Threads 16, and data fill to 0s instead of random.

The results of this experiment? Well, they appear to be rather stunning as the nature of L3 SRAM is that the memory is tiny but very fast and accessible to the CPU, so it can help load data locally before going to the system RAM. With AMD Ryzen 7 5800X3D, the speeds of this RAM disk are over 182 GB/s for reading and over 175 GB/s for writing. In another test, shared by Albert Thomas (@ultrawide219), we managed to see RAM disk based on AMD Ryzen 7800X3D V-Cache, which scores a little less with over 178 GB/s read and over 163 GB/s write speeds. Again, CrystalDiskMark only performed these tests on small allocations varying between 16 MiB and 32 MiB, so no real-world workloads are yet able to utilize this.
Source: via Tom's Hardware
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30 Comments on AMD 3D V-Cache RAM Disk Delivers Over 182 GB/s and 175 GB/s Read and Write Speeds

#26
THU31
And the sad thing is, if you put an Unreal Engine game on there, you'd still get shader compilation and traversal stutters. :D
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#27
TheGuruStud
DenverDamn... When I read the title, I was shocked and thought, "What product is AMD making now? A new type of SSD? What a bully wanting to succeed in all the areas that intel failed." But it's just a gimmick. :p:p
Theoretically, they could make an existing LGA chock full of these and stacked on each other as high as thermals allow (dual socket system). It would be so fast that your dick would fly off.
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#28
chrcoluk
This is very nice but I expect the advantage of cache is latency rather than the bandwidth.

Need a benchmark testing the latency compared to a normal RAM disk and I expect it will be blowing the RAM out of the water.
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#29
AnotherReader
Hardware1906so, the speed of these L3 cache is just fast as RAM
because right now, with quad channel 6000MHz DDR5, you can already reach 192GB/s
The L3 is vastly faster than DRAM. The figure in the CrystalDiskMark test is the bandwidth available to a single core from the L3. The bandwidth scales with the number of cores. A 7950X gets over 1800 GB/s from L3 with all cores reading from the L3. On the other hand, the 7950X only gets 72.85 GB/s from a 128-bit bus to DDR5-6000. Compare the throughput from a hypothetical 256-bit bus to that L3 result and you'll see why L3 is used. I haven't even touched upon the gap in latency between L3 and DRAM, but that one is even more insurmountable.

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#30
A Computer Guy
AnotherReaderThe L3 is vastly faster than DRAM. The figure in the CrystalDiskMark test is the bandwidth available to a single core from the L3. The bandwidth scales with the number of cores. A 7950X gets over 1800 GB/s from L3 with all cores reading from the L3. On the other hand, the 7950X only gets 72.85 GB/s from a 128-bit bus to DDR5-6000. Compare the throughput from a hypothetical 256-bit bus to that L3 result and you'll see why L3 is used. I haven't even touched upon the gap in latency between L3 and DRAM, but that one is even more insurmountable.

3950x wow. Still a great CPU.
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