On Mon, Jan 03, 2022 at 05:29:02PM +0100, Ingo Molnar wrote: > Yeah, so I *did* find this somewhat suboptimal too, and developed an > earlier version that used linker section tricks to gain the field offsets > more automatically. > > It was an unmitigated disaster: was fragile on x86 already (which has a zoo > of linking quirks with no precedent of doing this before bounds.c > processing), but on ARM64 and probably on most of the other RISC-ish > architectures there was also a real runtime code generation cost of using > linker tricks: 2-3 extra instructions per per_task() use - clearly > unacceptable. > > Found this out the hard way after making it boot & work on ARM64 and > looking at the assembly output, trying to figure out why the generated code > size increased. :-/ Right, I suggested you do the per-cpu thing. And then Mark reported that code-gen issue on arm64. I'm still thinking the toolchains ought to look at fixing that. It'll be too late to use for per-task, but at least the current per-cpu usages will (eventually) get better code-gen.
