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Modified discussion of privileges; added mention of RLIMIT_RTPRIO

This commit is contained in:
Michael Kerrisk 2005-07-28 14:37:51 +00:00
parent 0fdbc1eb4a
commit fd04afa828
1 changed files with 31 additions and 14 deletions
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45
man2/sched_setscheduler.2
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@ -33,7 +33,7 @@
.\" A couple of grammar clean-ups
.\" Modified 2004-05-27 by Michael Kerrisk <mtk-manpages@gmx.net>
.\"
.TH SETSCHEDULER 2 2004-05-27 "Linux 2.6.6" "Linux Programmer's Manual"
.TH SETSCHEDULER 2 2005-07-28 "Linux 2.6.12" "Linux Programmer's Manual"
.SH NAME
sched_setscheduler, sched_getscheduler \-
set and get scheduling algorithm/parameters
@ -94,10 +94,8 @@ intended for special time-critical applications that need precise
control over the way in which runnable processes are selected for
execution. Processes scheduled with \fISCHED_OTHER\fP must be assigned
the static priority 0, processes scheduled under \fISCHED_FIFO\fP or
\fISCHED_RR\fP can have a static priority in the range 1 to 99. Only
processes with superuser privileges can get a static priority higher
than 0 and can therefore be scheduled under \fISCHED_FIFO\fP or
\fISCHED_RR\fP. The system calls \fBsched_get_priority_min\fP and
\fISCHED_RR\fP can have a static priority in the range 1 to 99.
The system calls \fBsched_get_priority_min\fP and
\fBsched_get_priority_max\fP can be used to find out the valid
priority range for a scheduling policy in a portable way on all
POSIX.1b conforming systems.
@ -136,7 +134,6 @@ runnable processes with equal static priority. A \fISCHED_FIFO\fP
process runs until either it is blocked by an I/O request, it is
preempted by a higher priority process, or it calls \fBsched_yield\fP.
.SS SCHED_RR: Round Robin scheduling
\fISCHED_RR\fP is a simple enhancement of \fISCHED_FIFO\fP. Everything
described above for \fISCHED_FIFO\fP also applies to \fISCHED_RR\fP,
@ -163,6 +160,33 @@ each time quantum the process is ready to run, but denied to run by
the scheduler. This ensures fair progress among all \fISCHED_OTHER\fP
processes.
.SS Privileges and resource limits
A process calling
.BR sched_setscheduler
needs an effective user ID equal to the real user ID or effective
user ID of the process identified by
.IR pid ,
or it must be privileged (Linux: have the
.B CAP_SYS_NICE
capability).
In Linux kernels before 2.6.12, only privileged
.RB ( CAP_SYS_NICE )
processes can set a non-zero static priority.
Since Linux 2.6.12, the
.B RLIMIT_RTPRIO
resource limit defines a ceiling on the value to which an
unprivileged process can set a static priority for the
.B SCHED_RR
and
.BR SCHED_FIFO
policies.
See
.BR getrlimit (2)
for further information on
.BR RLIMIT_RTPRIO .
Privileged processes bypass this limit.
.SS Response time
A blocked high priority process waiting for the I/O has a certain
response time before it is scheduled again. The device driver writer
@ -219,14 +243,7 @@ or the parameter \fIp\fP does not make sense for the \fIpolicy\fP.
The calling process does not have appropriate privileges
(Linux: does not have the
.B CAP_SYS_NICE
capability). Only privileged processes are allowed to
activate the \fISCHED_FIFO\fP and \fISCHED_RR\fP
policies. A process calling
.BR sched_setscheduler
needs an effective user ID equal to the user ID or effective user ID
of the process identified by
.IR pid ,
or it must be privileged.
capability).
.TP
.B ESRCH
The process whose ID is \fIpid\fP could not be found.