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The code is much more readable and modular than you typical verilog dump, so it's probably the best CPU for microarchitecture experimentation. Source: did my master thesis prototyping a specialized cache. Started on Rocket Core, which turned out to be a total mess with all of the pipeline in a single module, basically impossible to introduce a new datapath without rewriting everything. Vex was a breath of fresh air. Spinal is also awesome, lots of QoL features for separating concerns between modules in a way that's impossible on Verilog and fixes lots of rough edges of Chisel.

Performance on FPGA was better than most open-source RISC-V cores out there as of 2020. Rocket might have been better on silicon, but that's it. I haven't looked much into it since then through.


Correctness is also distinct from applicability/usefulness. A program that lacks some important edge cases is marginally more useful than a program that takes impractical amount of time for most inputs. So "Correctness of a program is distinct from its performance" doesn't imply "performance is optional".

Unfortunately manifacturers almost always prefer price gouging on features that "CuStOmErS aRe NoT GoInG tO nEeD". Is it even a ZNS device available for someone who isn't a hyperscale datacenter operator nowadays?

Either you ask a manufacturer like WD, or you go to ebay AFAIK.

That said, ZNS is actually something specifically about being able to extract more value out of the same hardware (as the firmware no longer causes write amplification behind your back), which in turns means that the value for such a ZNS-capable drive ought to be strictly higher than for the traditional-only version with the same hardware.

And given that enterprise SSDs seem to only really get value from an OEM's holographic sticker on them (compare almost-new-grade used prices for those with the sticker on them vs. the just plain SSD/HDD original model number, missing the premium sticker), besides the common write-back-emergency capacitors that allow a physical write-back cache in the drive to ("safely") claim write-through semantics to the host, it should IMO be in the interest of the manufacturers to push ZNS:

ZNS makes, for ZNS-appropriate applications, the exact same hardware perform better despite requiring less fancy firmware. Also, especially, there's much less need for write-back cache as the drive doesn't sort individual random writes into something less prone to write amplification: the host software is responsible for sorting data together for minimizing write amplification (usually, arranging for data that will likely be deleted together to be physically in the same erasure block).

Also, I'm not sure how exactly "bad" bins of flash behave, but I'd not be surprised if ZNS's support for zones having less usable space than LBA/address range occupied (which can btw. change upon recycling/erasing the zone!) would allow rather poor quality flash to still be effectively utilized, as even rather unpredictable degradation can be handled this way. Basically, due to Copy-on-Write storage systems (like, Btrfs or many modern database backends (specifically, LSM-Tree ones)) inherently needing some slack/empty space, it's rather easy to cope with this space decreasing as a result of write operations, regardless of if the application/user data has actually grown from the writes: you just buy and add another drive/cluster-node when you run out of space, and until then, you can use 100% of the SSDs flash capacity, instead of up-front wasting capacity just to never have to decrease the drive's usable capacity over the warranty period.

That said: https://priceblaze.com/0TS2109-WesternDigital-Solid-State-Dr... claims (by part number) to be this model: https://www.westerndigital.com/en-ae/products/internal-drive... . That's about 150 $/TB. Refurbished; doesn't say how much life has been sucked out of them.

Give me, say, a Samsung 990 Pro 2 TB for 250 EUR but with firmware for ZNS-reformatting, instead of the 200 EUR MSRP/173 EUR Amazon.de price for the normal version.

Oh, and please let me use a decent portion of that 2 GB LPDDR4 as controller memory buffer at least if I'm in a ZNS-only formatting situation. It's after all not needed for keeping large block translation tables around, as ZNS only needs to track where physically a logical zone is currently located (wear leveling), and which individual blocks are marked dead in that physical zone (easy linear mapping between the non-contiguous usable physical blocks and the contiguous usable logical blocks). Beyond that, I guess technically it needs to keep track of open/closed zones and write pointers and filled/valid lengths.

Furthermore, I don't even need them to warranty the device lifespan in ZNS, only that it isn't bricked from activating ZNS mode. It would be nice to get as many drive-writes warranty as the non-ZNS version gets, though.


I know I might be barking up "just a showcase" tree, but what's the memory complexity of this? E g. a nice property of multipass assemblers is that these only need to keep a list of symbols in the memory rather than the whole program. Not really a concern for modern systems with large memories, but then those neat haskell tricks usually carry some extra O(n)s - in addition to (avoidable) extra constant factors due to hidden linked lists and immutability. Aka the infamous haskell quicksort - much shorter and clear, but also not really a quicksort.

Having fixed instruction length doesn't make the need to load large constants magically disappear. These just get split between multiple instructions. If anything, RISC-V might be worse. See also https://maskray.me/blog/2021-03-14-the-dark-side-of-riscv-li....

Somewhat tangential, cross-compilation seems to have been frowned upon in Unix historically. A lots of things out there just assume HOST==TARGET.

If you exit the program (as in the process) you don't need to free anything.

Energy-aware computing isn't about environmentalism and saving energy. It's sometimes framed as such in the name of greenwashing but it really isn't, the consumption was negligible before the AI/crypto craze. It's about "longer-lasting battery" and "getting more stuff on the chip without melting it".

Norway, no such thing here (at least not in smaller cities, not sure about Oslo). NTNU campus in Trondheim is warmed by waste heat from supercomputer exactly as GP suggested.

The average customer only exists in marketing people's heads.

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