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 @richfelker I don't really understand why on linux vdso gettimeofday() still requires a call when all it needs is a shmem read
@bofh453 @FioraAeterna Because it has nanosecond resolution not shitty timer interrupt resolution like Windows.
@RichFelker @FioraAeterna clock_gettime(CLOCK_REALTIME) does, neither gettimeofday() nor time() do & the former is often sufficient.
@RichFelker @FioraAeterna anyway I don't see why the resolution of the timer necessitates a f'n call instead of a mem read to get its value.
@bofh453 @FioraAeterna Who is going to write a new time value to memory 1 billion times per second?
@richfelker @fioraaeterna oh, the HPET device doesn't memory-map its value register?
@bofh453 @FioraAeterna It might, but then applications can't run on machines without HPET. With a func ptr, OTOH, fallback is possible.
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