NAME

gsched — control utility for disk scheduler GEOM class

SYNOPSIS

DESCRIPTION

The gsched utility (also callable as geom sched ...) changes the scheduling policy of the requests going to a provider.

The first argument to gsched indicates an action to be performed:

create

Create a new provider and geom node using the specified scheduling algorithm. algorithm is the name of the scheduling algorithm used for the provider. Available algorithms include: rr, which implements anticipatory scheduling with round robin service among clients; as, which implements a simple form of anticipatory scheduling with no per-client queue.

If the operation succeeds, the new provider should appear with name /dev/⟨dev⟩.sched.. The kernel module geom_sched.ko will be loaded if it is not loaded already.

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.

A subsequent "destroy" will remove the newly created geom and hook the provider back to the original geom.

configure

Configure existing scheduling provider. It supports the same options as the create command.

destroy

Destroy the geom specified in the parameter.

reset

Do nothing.

list | status | load | unload

See geom(8).

Additional options:

-f

Force the removal of the specified provider.

-v

Be more verbose.

SYSCTL VARIABLES

The following sysctl(8) variables can be used to control the behavior of the SCHED GEOM class. The default value is shown next to each variable.

kern.geom.sched.debug: 0

Debug level of the 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.

EXIT STATUS

Exit status is 0 on success, and 1 if the command fails.

EXAMPLES

The following example shows how to create a scheduling provider for disk /dev/ada0, and how to destroy it.

# 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.

SEE ALSO

geom(4), geom(8)

HISTORY

The gsched utility first appeared in FreeBSD 8.1.

AUTHORS

Fabio Checconi <fabio@FreeBSD.org>
Luigi Rizzo <luigi@FreeBSD.org>