On the design of the SYSENTER Intel syscall instruction, and how the elegant idea fell apart https://groups.google.com/forum/m/#!topic/comp.arch/CjDs4MJCBow%5B1-25%5D …pic.twitter.com/VIZlsh87cE
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On the design of the SYSENTER Intel syscall instruction, and how the elegant idea fell apart https://groups.google.com/forum/m/#!topic/comp.arch/CjDs4MJCBow%5B1-25%5D …pic.twitter.com/VIZlsh87cE
@FioraAeterna Why does anyone care about SYSENTER being 2 vs 15 cycles when kernel entry/exit overhead is 500-1000 cycles? :-(
@RichFelker because a lot of common syscalls, like say fetching time, require no security checks and can be done in a few cycles
@RichFelker presumably someone had a dream for making syscalls less horrible and the dream slowly shattered
@FioraAeterna My view is just that software arch., not hw/insn timings, is the overwhelmingly dominating factor limiting syscall perf.
@FioraAeterna One big problem is that the Linux syscall ABI makes all registers call-saved, so they have to save/restore any kernel may use.
@RichFelker reminds me of one of the many strategies Synthesis OS (http://valerieaurora.org/synthesis/SynthesisOS/ …) used to avoid syscall overhead
@RichFelker it JIT-compiled syscall functions to avoid unnecessary paths, including minimal register saving/restoring
@FioraAeterna Just something like entry point in C with attribute((interrupt)) & LTO in theory could achieve the same.
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