On Thu, May 11, 2023 at 01:33:12AM -0400, Theodore Ts'o wrote: > Seriously, does this mean that bcachefs won't work on Arm systems > (arm32 or arm64)? Or Risc V systems? Or S/390's? Or Power > architectuers? Or Itanium or PA-RISC systems? (OK, I really don't > care all that much about those last two. :-) No :) My CI servers are arm64 servers. There's a bch2_bkey_unpack_key() written in C, that works on any architecture. But specializing for a particular format is a not-insignificant performance improvement, so writing an arm64 version has been on my todo list. > When people ask me why file systems are so hard to make enterprise > ready, I tell them to recall the general advice given to people to > write secure, robust systems: (a) avoid premature optimization, (b) > avoid fine-grained, multi-threaded programming, as much as possible, > because locking bugs are a b*tch, and (c) avoid unnecessary global > state as much as possible. > > File systems tend to violate all of these precepts: (a) people chase > benchmark optimizations to the exclusion of all else, because people > have an unhealthy obsession with Phornix benchmark articles, (b) file > systems tend to be inherently multi-threaded, with lots of locks, and > (c) file systems are all about managing global state in the form of > files, directories, etc. > > However, hiding a miniature architecture-specific compiler inside a > file system seems to be a rather blatent example of "premature > optimization". Ted, this project is _15_ years old. I'm getting ready to write a full explanation of what this is for and why it's important, I've just been busy with the conference - and I want to write something good, that provides all the context. I've also been mulling over fallback options, but I don't see any good ones. The unspecialized, C version of unpack has branches (the absolute minimum, I took my time when I was writing that code too); the specialized versions are branchless and _much_ smaller, and the only way to do that specialization is with some form of dynamic codegen. But I do owe you all a detailed walkthrough of what this is all about, so you'll get it in the next day or so. Cheers, Kent
