potential discontinuities in our UTC timescale.
Applications can monitor this variable if they want to be informed
about steps in the timescale. Slews (ntp and adjtime(2)) and
frequency adjustments (ntp) will not increment this counter, only
operations which set the clock. No attempt is made to classify
size or direction of the step.
called. Otherwise (depending on a non-deterministic sort), the timecounter
code can be initialized before the clock rate has been set (on ia64) and it
assumes hz = 100, rather than the real value of 1024. I'm not sure how much
gets upset by this.
Glanced at by: phk
functions which run for several milliseconds at a time and getting
in queue behind one or more of those makes us miss our rewind.
Instead call it from hardclock() like we used to do, but retain the
prescaler so we still cope with high HZ values.
by other bits of code, split struct timecounter into two.
struct timecounter contains just the bits which pertains to the hardware
counter and the reading of it.
struct timehands (as in "the hands on a clock") contains all the ugly bit
fidling stuff. Statically compile ten timehands.
This commit is the functional part. A later cosmetic patch will rename
various variables and fieldnames.
timeout loop.
Limit the rate at which we wind the timecounters to approx 1000 Hz.
This limits the precision of the get{bin,nano,micro}[up]time(9)
functions to roughly a millisecond.
timecounter will be used starting at the next second, which is
good enough for sysctl purposes. If better adjustment is needed
the NTP PLL should be used.
Apply the change as a continuous slew rather than as a series of
discrete steps and make it possible to adjust arbitraryly huge
amounts of time in either direction.
In practice this is done by hooking into the same once-per-second
loop as the NTP PLL and setting a suitable frequency offset deducting
the amount slewed from the remainder. If the remaining delta is
larger than 1 second we slew at 5000PPM (5msec/sec), for a delta
less than a second we slew at 500PPM (500usec/sec) and for the last
one second period we will slew at whatever rate (less than 500PPM)
it takes to eliminate the delta entirely.
The old implementation stepped the clock a number of microseconds
every HZ to acheive the same effect, using the same rates of change.
Eliminate the global variables tickadj, tickdelta and timedelta and
their various use and initializations.
This removes the most significant obstacle to running timecounter and
NTP housekeeping from a timeout rather than hardclock.
our feet when we look inside timecounter structures.
Make the "sync_other" code more robust by never overwriting the
tc_next field.
Add counters for the bin[up]time functions.
Call tc_windup() in tc_init() and switch_timecounter() to make sure
we all the fields set right.
The binary format "bintime" is a 32.64 format, it will go to 64.64
when time_t does.
The bintime format is available to consumers of time in the kernel,
and is preferable where timeintervals needs to be accumulated.
This change simplifies much of the magic math inside the timecounters
and improves the frequency and time precision by a couple of bits.
I have not been able to measure a performance difference which was not
a tiny fraction of the standard deviation on the measurements.
HZ=BIGNUM will strain the assumptions behind timecounters to the
point where they break.
This may or may not help people seeing microuptime() backwards messages.
Make the global timecounter variable volatile, it makes no difference in
the code GCC generates, but it makes represents the intent correctly.
Thanks to: jdp
MFC after: 2 weeks
include:
* Mutual exclusion is used instead of spl*(). See mutex(9). (Note: The
alpha port is still in transition and currently uses both.)
* Per-CPU idle processes.
* Interrupts are run in their own separate kernel threads and can be
preempted (i386 only).
Partially contributed by: BSDi (BSD/OS)
Submissions by (at least): cp, dfr, dillon, grog, jake, jhb, sheldonh
Make the public interface more systematically named.
Remove the alternate method, it doesn't do any good, only ruins performance.
Add counters to profile the usage of the 8 access functions.
Apply the beer-ware to my code.
The weird +/- counts are caused by two repocopies behind the scenes:
kern/kern_clock.c -> kern/kern_tc.c
sys/time.h -> sys/timetc.h
(thanks peter!)
and extend. The new function containing the code is named schedclock()
as in NetBSD, but it has slightly different semantics (it already handles
incrementation of p->p_cpticks, and it should handle any calling frequency).
Agreed with in principle by: dufault
NOTE: This will break building ntpd until ntpd has been upgraded to also
support draft 05. People that want to build ntpd in the meantime can
get patches from me.
