.\" Copyright (c) 2009-2010 Fabio Checconi
.\" Copyright (c) 2009-2010 Luigi Rizzo, Universita` di Pisa
.\" All rights reserved.
.\"
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.\" $FreeBSD$
.\"
.Dd July 26, 2012
.Dt GSCHED 8
.Os
.Sh NAME
.Nm gsched
.Nd "control utility for disk scheduler GEOM class"
.Sh SYNOPSIS
.Nm
.Cm create
.Op Fl v
.Op Fl a Ar algorithm
.Ar provider ...
.Nm
.Cm insert
.Op Fl v
.Op Fl a Ar algorithm
.Ar provider ...
.Nm
.Cm configure
.Op Fl v
.Op Fl a Ar algorithm
.Ar node ...
.Nm
.Cm destroy
.Op Fl fv
.Ar node ...
.Nm
.Cm reset
.Op Fl v
.Ar node ...
.Nm
.Cm { list | status | load | unload }
.Sh DESCRIPTION
The
.Nm
utility (also callable as
.Nm geom sched ... )
changes the scheduling policy of the requests going to a provider.
.Pp
The first argument to
.Nm
indicates an action to be performed:
.Bl -tag -width ".Cm configure"
.It Cm create
Create a new provider and geom node using the specified scheduling algorithm.
.Ar algorithm
is the name of the scheduling algorithm used for the provider.
Available algorithms include:
.Ar rr ,
which implements anticipatory scheduling with round robin service
among clients;
.Ar as ,
which implements a simple form of anticipatory scheduling with
no per-client queue.
.Pp
If the operation succeeds, the new provider should appear with name
.Pa /dev/ Ns Ao Ar dev Ac Ns Pa .sched. .
The kernel module
.Pa geom_sched.ko
will be loaded if it is not loaded already.
.It Cm insert
Operates as "create", but the insertion is "transparent",
i.e. the existing provider is rerouted to the newly created geom,
which in turn forwards requests to the existing geom.
This operation allows one to start/stop a scheduling service
on an already existing provider.
.Pp
A subsequent "destroy" will remove the newly created geom and
hook the provider back to the original geom.
.It Cm configure
Configure existing scheduling provider.  It supports the same options
as the
.Nm create
command.
.It Cm destroy
Destroy the geom specified in the parameter.
.It Cm reset
Do nothing.
.It Cm list | status | load | unload
See
.Xr geom 8 .
.El
.Pp
Additional options:
.Bl -tag -width ".Fl f"
.It Fl f
Force the removal of the specified provider.
.It Fl v
Be more verbose.
.El
.Sh SYSCTL VARIABLES
The following
.Xr sysctl 8
variables can be used to control the behavior of the
.Nm SCHED
GEOM class.
The default value is shown next to each variable.
.Bl -tag -width indent
.It Va kern.geom.sched.debug : No 0
Debug level of the
.Nm SCHED
GEOM class.
This can be set to a number between 0 and 2 inclusive.
If set to 0 minimal debug information is printed, and if set to 2 the
maximum amount of debug information is printed.
.El
.Sh EXIT STATUS
Exit status is 0 on success, and 1 if the command fails.
.Sh EXAMPLES
The following example shows how to create a scheduling provider for disk
.Pa /dev/ada0 ,
and how to destroy it.
.Bd -literal -offset indent
# Load the geom_sched module:
kldload geom_sched
# Load some scheduler classes used by geom_sched:
kldload gsched_rr
# Configure device ada0 to use scheduler "rr":
geom sched insert -a rr ada0
# Now provider ada0 uses the "rr" algorithm;
# the new geom is ada0.sched.
# Remove the scheduler on the device:
geom sched destroy -v ada0.sched.
.Ed
.Sh SEE ALSO
.Xr geom 4 ,
.Xr geom 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 8.1 .
.Sh AUTHORS
.An Fabio Checconi Aq fabio@FreeBSD.org
.An Luigi Rizzo Aq luigi@FreeBSD.org