CVSROOT: /cvs
Module name: src
Changes by: chel...@cvs.openbsd.org 2019/12/24 17:15:36
Modified files:
sbin/sysctl : sysctl.c
sys/sys : timeout.h
sys/kern : kern_timeout.c
Log message:
timeout(9): new flag: TIMEOUT_SCHEDULED, new statistic: tos_scheduled
This flag is set whenever a timeout is put on the wheel and cleared upon
(a) running, (b) deletion, and (c) readdition. It serves two purposes:
1. Facilitate distinguishing scheduled and rescheduled timeouts. When a
timeout is put on the wheel it is "scheduled" for a later softclock().
If this happens two or more times it is also said to be "rescheduled".
The tos_rescheduled value thus indicates how many distant timeouts
have been cascaded into a lower wheel level.
2. Eliminate false late timeouts. A timeout is not late if it is due
before softclock() has had a chance to schedule it. To track this we
need additional state, hence a new flag.
rprocter@ raises some interesting questions. Some answers:
- This interface is not stable and name changes are possible at a
later date.
- Although rescheduling timeouts is a side effect of the underlying
implementation, I don't forsee us using anything but a timeout wheel
in the future. Other data structures are too slow in practice, so
I doubt that the concept of a rescheduled timeout will be irrelevant
any time soon.
- I think the development utility of gathering these sorts of statistics
is high. Watching the distribution of timeouts under a given workflow
is informative.
ok visa@
