ae6222b0c3
Reviewed by: rgrimes MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D19485
276 lines
7.7 KiB
Groff
276 lines
7.7 KiB
Groff
.\" Copyright (c) 2000-2001 John H. Baldwin <jhb@FreeBSD.org>
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd November 3, 2000
|
|
.Dt SCHEDULER 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm curpriority_cmp ,
|
|
.Nm maybe_resched ,
|
|
.Nm resetpriority ,
|
|
.Nm roundrobin ,
|
|
.Nm roundrobin_interval ,
|
|
.Nm sched_setup ,
|
|
.Nm schedclock ,
|
|
.Nm schedcpu ,
|
|
.Nm setrunnable ,
|
|
.Nm updatepri
|
|
.Nd perform round-robin scheduling of runnable processes
|
|
.Sh SYNOPSIS
|
|
.In sys/param.h
|
|
.In sys/proc.h
|
|
.Ft int
|
|
.Fn curpriority_cmp "struct proc *p"
|
|
.Ft void
|
|
.Fn maybe_resched "struct thread *td"
|
|
.Ft void
|
|
.Fn propagate_priority "struct proc *p"
|
|
.Ft void
|
|
.Fn resetpriority "struct ksegrp *kg"
|
|
.Ft void
|
|
.Fn roundrobin "void *arg"
|
|
.Ft int
|
|
.Fn roundrobin_interval "void"
|
|
.Ft void
|
|
.Fn sched_setup "void *dummy"
|
|
.Ft void
|
|
.Fn schedclock "struct thread *td"
|
|
.Ft void
|
|
.Fn schedcpu "void *arg"
|
|
.Ft void
|
|
.Fn setrunnable "struct thread *td"
|
|
.Ft void
|
|
.Fn updatepri "struct thread *td"
|
|
.Sh DESCRIPTION
|
|
Each process has three different priorities stored in
|
|
.Vt "struct proc" :
|
|
.Va p_usrpri ,
|
|
.Va p_nativepri ,
|
|
and
|
|
.Va p_priority .
|
|
.Pp
|
|
The
|
|
.Va p_usrpri
|
|
member is the user priority of the process calculated from a process'
|
|
estimated CPU time and nice level.
|
|
.Pp
|
|
The
|
|
.Va p_nativepri
|
|
member is the saved priority used by
|
|
.Fn propagate_priority .
|
|
When a process obtains a mutex, its priority is saved in
|
|
.Va 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
|
|
.Va p_nativepri .
|
|
.Pp
|
|
The
|
|
.Va p_priority
|
|
member is the actual priority of the process and is used to determine what
|
|
.Xr runqueue 9
|
|
it runs on, for example.
|
|
.Pp
|
|
The
|
|
.Fn 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
|
|
.Fn curpriority_cmp
|
|
will return zero.
|
|
The cached priority of the currently running process is updated when a process
|
|
resumes from
|
|
.Xr tsleep 9
|
|
or returns to userland in
|
|
.Fn userret
|
|
and is stored in the private variable
|
|
.Va curpriority .
|
|
.Pp
|
|
The
|
|
.Fn 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
|
|
.Dv KEF_NEEDRESCHED
|
|
is set.
|
|
.Pp
|
|
The
|
|
.Fn 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
|
|
.Xr runqueue 9 ,
|
|
then the process is moved to the appropriate
|
|
.Xr 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.
|
|
.Pp
|
|
The
|
|
.Fn resetpriority
|
|
function recomputes the user priority of the ksegrp
|
|
.Fa kg
|
|
(stored in
|
|
.Va kg_user_pri )
|
|
and calls
|
|
.Fn maybe_resched
|
|
to force a reschedule of each thread in the group if needed.
|
|
.Pp
|
|
The
|
|
.Fn roundrobin
|
|
function is used as a
|
|
.Xr timeout 9
|
|
function to force a reschedule every
|
|
.Va sched_quantum
|
|
ticks.
|
|
.Pp
|
|
The
|
|
.Fn roundrobin_interval
|
|
function simply returns the number of clock ticks in between reschedules
|
|
triggered by
|
|
.Fn roundrobin .
|
|
Thus, all it does is return the current value of
|
|
.Va sched_quantum .
|
|
.Pp
|
|
The
|
|
.Fn sched_setup
|
|
function is a
|
|
.Xr SYSINIT 9
|
|
that is called to start the callout driven scheduler functions.
|
|
It just calls the
|
|
.Fn roundrobin
|
|
and
|
|
.Fn 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.
|
|
.Pp
|
|
The
|
|
.Fn schedclock
|
|
function is called by
|
|
.Fn 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
|
|
.Fn resetpriority .
|
|
.Pp
|
|
The
|
|
.Fn 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
|
|
.Xr runqueue 9
|
|
if necessary.
|
|
Thirdly, it updates the %CPU estimate used by utilities such as
|
|
.Xr ps 1
|
|
and
|
|
.Xr top 1
|
|
so that 95% of the CPU usage is forgotten in 60 seconds.
|
|
Once all process priorities have been updated,
|
|
.Fn schedcpu
|
|
calls
|
|
.Fn vmmeter
|
|
to update various other statistics including the load average.
|
|
Finally, it schedules itself to run again in
|
|
.Va hz
|
|
clock ticks.
|
|
.Pp
|
|
The
|
|
.Fn setrunnable
|
|
function is used to change a process's state to be runnable.
|
|
The process is placed on a
|
|
.Xr 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
|
|
.Fn schedcpu ,
|
|
then
|
|
.Fn updatepri
|
|
is used to adjust the priority of the process.
|
|
.Pp
|
|
The
|
|
.Fn 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
|
|
.Fn schedcpu
|
|
event that the process was asleep.
|
|
Finally, it calls
|
|
.Fn resetpriority
|
|
to adjust the priority of the process.
|
|
.Sh SEE ALSO
|
|
.Xr mi_switch 9 ,
|
|
.Xr runqueue 9 ,
|
|
.Xr sleepqueue 9 ,
|
|
.Xr tsleep 9
|
|
.Sh BUGS
|
|
The
|
|
.Va curpriority
|
|
variable really should be per-CPU.
|
|
In addition,
|
|
.Fn maybe_resched
|
|
should compare the priority of
|
|
.Fa chk
|
|
with that of each CPU, and then send an IPI to the processor with the lowest
|
|
priority to trigger a reschedule if needed.
|
|
.Pp
|
|
Priority propagation is broken and is thus disabled by default.
|
|
The
|
|
.Va 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
|
|
.Va p_nativepri
|
|
will be clobbered.
|