Messages in this thread | | | Date | Mon, 10 Jan 2022 11:28:01 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell" |
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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.
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