Партнёры:
Хостинг:
curpriority_cmp maybe_resched resetpriority roundrobin roundrobin_interval sched_setup schedclock schedcpu setrunnable updatepri - perform round-robin scheduling of runnable processes
The p_usrpri member is the user priority of the process calculated from a process' estimated CPU time and nice level.
The
p_nativepri
member is the saved priority used by
propagate_priority (.);
When a process obtains a mutex, its priority is saved in
p_nativepri
While it holds the mutex, the process's priority may be bumped by another
process that blocks on the mutex.
When the process releases the mutex, then its priority is restored to the
priority saved in
p_nativepri
The p_priority member is the actual priority of the process and is used to determine what runqueue(9) it runs on, for example.
The
curpriority_cmp ();
function compares the cached priority of the currently running process with
process
Fa p .
If the currently running process has a higher priority, then it will return
a value less than zero.
If the current process has a lower priority, then it will return a value
greater than zero.
If the current process has the same priority as
Fa p ,
then
curpriority_cmp ();
will return zero.
The cached priority of the currently running process is updated when a process
resumes from
tsleep(9)
or returns to userland in
userret ();
and is stored in the private variable
curpriority
The
maybe_resched ();
function compares the priorities of the current thread and
Fa td .
If
Fa td
has a higher priority than the current thread, then a context switch is
needed, and
KEF_NEEDRESCHED
is set.
The
propagate_priority ();
looks at the process that owns the mutex
Fa p
is blocked on.
That process's priority is bumped to the priority of
Fa p
if needed.
If the process is currently running, then the function returns.
If the process is on a
runqueue(9),
then the process is moved to the appropriate
runqueue(9)
for its new priority.
If the process is blocked on a mutex, its position in the list of
processes blocked on the mutex in question is updated to reflect its new
priority.
Then, the function repeats the procedure using the process that owns the
mutex just encountered.
Note that a process's priorities are only bumped to the priority of the
original process
Fa p ,
not to the priority of the previously encountered process.
The
resetpriority ();
function recomputes the user priority of the ksegrp
Fa kg
(stored in
kg_user_pri
and calls
maybe_resched ();
to force a reschedule of each thread in the group if needed.
The
roundrobin ();
function is used as a
timeout(9)
function to force a reschedule every
sched_quantum
ticks.
The
roundrobin_interval ();
function simply returns the number of clock ticks in between reschedules
triggered by
roundrobin (.);
Thus, all it does is return the current value of
sched_quantum
The
sched_setup ();
function is a
SYSINIT(9)
that is called to start the callout driven scheduler functions.
It just calls the
roundrobin ();
and
schedcpu ();
functions for the first time.
After the initial call, the two functions will propagate themselves by
registering their callout event again at the completion of the respective
function.
The
schedclock ();
function is called by
statclock ();
to adjust the priority of the currently running thread's ksegrp.
It updates the group's estimated CPU time and then adjusts the priority via
resetpriority (.);
The
schedcpu ();
function updates all process priorities.
First, it updates statistics that track how long processes have been in various
process states.
Secondly, it updates the estimated CPU time for the current process such
that about 90% of the CPU usage is forgotten in 5 * load average seconds.
For example, if the load average is 2.00,
then at least 90% of the estimated CPU time for the process should be based
on the amount of CPU time the process has had in the last 10 seconds.
It then recomputes the priority of the process and moves it to the
appropriate
runqueue(9)
if necessary.
Thirdly, it updates the %CPU estimate used by utilities such as
ps(1)
and
top(1)
so that 95% of the CPU usage is forgotten in 60 seconds.
Once all process priorities have been updated,
schedcpu ();
calls
vmmeter ();
to update various other statistics including the load average.
Finally, it schedules itself to run again in
hz
clock ticks.
The
setrunnable ();
function is used to change a process's state to be runnable.
The process is placed on a
runqueue(9)
if needed, and the swapper process is woken up and told to swap the process in
if the process is swapped out.
If the process has been asleep for at least one run of
schedcpu (,);
then
updatepri ();
is used to adjust the priority of the process.
The
updatepri ();
function is used to adjust the priority of a process that has been asleep.
It retroactively decays the estimated CPU time of the process for each
schedcpu ();
event that the process was asleep.
Finally, it calls
resetpriority ();
to adjust the priority of the process.
Priority propagation is broken and is thus disabled by default. The p_nativepri variable is only updated if a process does not obtain a sleep mutex on the first try. Also, if a process obtains more than one sleep mutex in this manner, and had its priority bumped in between, then p_nativepri will be clobbered.
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