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
Thegsched 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
createcommand. 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
SCHEDGEOM 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
HISTORY
The gsched utility first appeared in
FreeBSD 8.1.
AUTHORS
Fabio Checconi
<fabio@FreeBSD.org>
Luigi Rizzo
<luigi@FreeBSD.org>