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by ohazi 2173 days ago
> Writing software on ARM laptops that are deployed to production servers running on x86 servers will start to cause a host of new challenges.

We already know what this is like, and the challenges are usually in the other direction (write/test on x86, attempt to deploy on ARM).

This is due to things like word alignment and memory ordering requirements. For the most part, the "extra complexity" in x86 allows you to ignore a lot of the stuff you need to pay more attention to on ARM.
1 comments
scarface74 2173 days ago
Millions of iOS developers develop on x86 and deploy to ARM devices every day. The iOS simulator compiles apps to x86 and they run on top of an x86 version of the iOS frameworks.
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ohazi 2173 days ago
The "x86 version of the iOS frameworks" is where those differences would be apparent. Apple may have done a good job with their simulator, but that's just it -- Apple did this work so that their iOS developers wouldn't have to.

As an iOS developer, you don't need to think about memory barriers if you don't want to, but Apple's simulator and frameworks absolutely do. That's the kind of work that awaits systems programmers who want to port high performance x86 server software to ARM.

x86 hardware is physically more permissive than ARM. Accesses that must be aligned on ARM can be left unaligned on x86, and they'll still work correctly. But x86 isn't going to explode either if you do happen align them. ARM is weakly ordered, x86 is strongly ordered, so you generally need more fences on ARM than you do on x86, but leaving these fences in place doesn't break things on x86.

My point was that code that works correctly on ARM usually works correctly without modification on x86. The opposite is generally not the case, even if the iOS simulator hides this for you.

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vbezhenar 2172 days ago
People use Java and Go to write server software. They'll make things aligned properly, so it won't be a problem.

The real problem is memory concurrency model. You will hit subtle concurrency bugs with ARM which were not manifested on x86. And those bugs will be present in any language with threads and shared data. They are hard to debug and frustrating, because they'll lead to rare deadlocks, and resource leaks.

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