GSCHED(8)

NAME
gsched - control utility for disk scheduler GEOM class

SYNOPSIS
gsched create [-v] [-a algorithm] provider ...
gsched insert [-v] [-a algorithm] provider ...
gsched configure [-v] [-a algorithm] node ...
gsched destroy [-fv] node ...
gsched reset [-v] node ...
gsched { list | status | load | unload }

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/ad0, and how to destroy it.

    # Load the geom_sched module:
    kldload geom_sched
    # Load some scheduler classes used by geom_sched:
    kldload gsched_rr gsched_as
    # Configure device ad0 to use scheduler "rr":
    geom sched insert -a rr ad0
    # Now provider ad0 uses the "rr" algorithm;
    # the new geom is ad0.sched.
    # Remove the scheduler on the device:
    geom sched destroy -v ad0.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>