Author :
cheloha
Date :
2020-06-24 22:03:40
Hash :3209772d Message :kernel: use gettime(9)/getuptime(9) in lieu of time_second(9)/time_uptime(9)
time_second(9) and time_uptime(9) are widely used in the kernel to
quickly get the system UTC or system uptime as a time_t. However,
time_t is 64-bit everywhere, so it is not generally safe to use them
on 32-bit platforms: you have a split-read problem if your hardware
cannot perform atomic 64-bit reads.
This patch replaces time_second(9) with gettime(9), a safer successor
interface, throughout the kernel. Similarly, time_uptime(9) is replaced
with getuptime(9).
There is a performance cost on 32-bit platforms in exchange for
eliminating the split-read problem: instead of two register reads you
now have a lockless read loop to pull the values from the timehands.
This is really not *too* bad in the grand scheme of things, but
compared to what we were doing before it is several times slower.
There is no performance cost on 64-bit (__LP64__) platforms.
With input from visa@, dlg@, and tedu@.
Several bugs squashed by visa@.
ok kettenis@
cheloha