95 lines
3.6 KiB
Groff
95 lines
3.6 KiB
Groff
.TH ionice "1" "August 2005" ionice
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.SH NAME
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ionice \- get/set program io scheduling class and priority
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.SH SYNOPSIS
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.B ionice
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.RB [[ \-c
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.IR class ]
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.RB [ \-n
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.IR classdata ]
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.RB [ \-t ]]
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.BI \-p \ PID
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.RI [ PID ]...
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.br
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.B ionice
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.RB [ \-c
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.IR class ]
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.RB [ \-n
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.IR classdata ]
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.RB [ \-t ]
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.IR COMMAND\ [ ARG ]...
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.SH DESCRIPTION
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This program sets or gets the io scheduling class and priority for a program.
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If no arguments or just \fB\-p\fR is given, \fBionice\fR will query the current
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io scheduling class and priority for that process.
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As of this writing, a process can be in one of three scheduling classes:
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.IP "\fBIdle\fP"
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A program running with idle io priority will only get disk time when no other
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program has asked for disk io for a defined grace period. The impact of idle
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io processes on normal system activity should be zero. This scheduling
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class does not take a priority argument. Presently, this scheduling class
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is permitted for an ordinary user (since kernel 2.6.25).
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.IP "\fBBest effort\fP"
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This is the effective scheduling class for any process that has not asked for
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a specific io priority.
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This class takes a priority argument from \fI0-7\fR, with lower
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number being higher priority. Programs running at the same best effort
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priority are served in a round-robin fashion.
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Note that before kernel 2.6.26 a process that has not asked for an io priority
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formally uses "\fBnone\fP" as scheduling class, but the io scheduler will treat
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such processes as if it were in the best effort class. The priority within the
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best effort class will be dynamically derived from the cpu nice level of the
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process: io_priority = (cpu_nice + 20) / 5.
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For kernels after 2.6.26 with CFQ io scheduler a process that has not asked for
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an io priority inherits CPU scheduling class. The io priority is derived from
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the cpu nice level of the process (same as before kernel 2.6.26).
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.IP "\fBReal time\fP"
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The RT scheduling class is given first access to the disk, regardless of
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what else is going on in the system. Thus the RT class needs to be used with
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some care, as it can starve other processes. As with the best effort class,
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8 priority levels are defined denoting how big a time slice a given process
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will receive on each scheduling window. This scheduling class is not
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permitted for an ordinary (i.e., non-root) user.
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.SH OPTIONS
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.IP "\fB-c \fIclass\fP"
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The scheduling class. \fI0\fR for none, \fI1\fR for real time, \fI2\fR for
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best-effort, \fI3\fR for idle.
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.IP "\fB-n \fIclassdata\fP"
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The scheduling class data. This defines the class data, if the class
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accepts an argument. For real time and best-effort, \fI0-7\fR is valid
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data.
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.IP "\fB-p \fIpid\fP"
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Pass in process PID(s) to view or change already running processes. If this argument
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is not given, \fBionice\fP will run the listed program with the given
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parameters.
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.IP "\fB-t\fP"
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Ignore failure to set requested priority. If COMMAND or PID(s) is specified, run it
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even in case it was not possible to set desired scheduling priority, what
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can happen due to insufficient privileges or old kernel version.
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.SH EXAMPLES
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.LP
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.TP 7
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# \fBionice\fP -c 3 -p 89
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.TP 7
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Sets process with PID 89 as an idle io process.
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.TP 7
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# \fBionice\fP -c 2 -n 0 bash
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.TP 7
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Runs 'bash' as a best-effort program with highest priority.
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.TP 7
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# \fBionice\fP -p 89 91
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.TP 7
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Prints the class and priority of the processes with PID 89 and 91.
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.SH NOTES
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Linux supports io scheduling priorities and classes since 2.6.13 with the CFQ
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io scheduler.
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.SH AUTHORS
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Jens Axboe <jens@axboe.dk>
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.SH AVAILABILITY
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The ionice command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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