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
@FioraAeterna On Linux that works via never entering kernel, using vdso. Linux has no fastpath for real syscalls tho. Even getpid is 500+ ns
@RichFelker that's incredible
and if someone says "that's slow as molasses" people just say "well don't call it as much"
@FioraAeterna glibc actually caches the getpid result for this reason. But there are nasty issues invalidating the cached value @ fork/clone
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