[flimflamm]

Is this just buttering the cost of switches by crippling the optimization options compiler have?

[lukaslalinsky]

If this was done the classical C way, you would always have to stack-save a number of registers, even if they are not really needed. The only difference here is that the compiler will do the save for you, in whatever way fits the context best. Sometimes it will stack-save, sometimes it will decide to use a different option. It's always strictly better than explicitly saving/restoring N registers unaware of the context. Keep in mind, that in Zig, the compiler always knows the entire code base. It does not work on object/function boundaries. That leads to better optimizations.

[hawk_]

This is amazing to me that you can do this in Zig code directly as opposed to messing with the compiler.

[GoblinSlayer]

I wonder how you see it. Stackful coroutines switch context on syscall in the top stack frame, the deeper frames are regular optimized code, but syscall/sysret is already big context switch. And read/epoll loop has exactly same structure, the point of async programming isn't optimization of computation, but optimization of memory consumption. Performance is determined by features and design (and Electron).

[hawk_]

What do you mean by "buttering the cost of switches", can you elaborate? (I am trying to learn about this topic)

[masfuerte]

I think it is

> buttering the cost of switches [over the whole execution time]

The switches get cheaper but the rest of the code gets slower (because it has less flexibility in register allocation) so the cost of the switches is "buttered" (i.e. smeared) over the rest of the execution time.

But I don't think this argument holds water. The surrounding code can use whatever registers it wants. In the worst case it saves and restores all of them, which is what a standard context switch does anyway. In other words, this can be better and is never worse.