Overview
This document describes SLURM scheduler plugins and the API that defines
them. It is intended as a resource to programmers wishing to write their own SLURM
scheduler plugins. This is version 0 of the API.
It is noteworthy that two different models are used for job scheduling.
The backfill scheduler lets SLURM establish the initial job priority
and can periodically alter job priorities to change their order within the queue.
The wiki scheduler establishes an initial priority of zero (held) for
all jobs. These jobs only begin execution when the wiki scheduler
explicitly raises the their priority (releasing them).
Developers may use the model that best fits their needs.
Note that a separate node selection plugin
is available for controlling that aspect of scheduling.
SLURM scheduler plugins are SLURM plugins that implement the SLURM scheduler
API described herein. They must conform to the SLURM Plugin API with the following
specifications:
const char plugin_type[]
The major type must be "sched." The minor type can be any recognizable
abbreviation for the type of scheduler. We recommend, for example:
- builtinA plugin that implements the API without providing any actual
scheduling services. This is the default behavior and implements first-in-first-out scheduling.
- backfillRaise the priority of jobs if doing so results in their starting earlier
without any delay in the expected initiation time of any higher priority job.
- wikiUse The Maui Scheduler
(Wiiki version) as an external entity to control SLURM job scheduling.
The plugin_name and
plugin_version
symbols required by the SLURM Plugin API require no specialization for scheduler support.
Note carefully, however, the versioning discussion below.
The programmer is urged to study
src/plugins/sched/backfill and
src/plugins/sched/builtin
for sample implementations of a SLURM scheduler plugin.
Data Objects
The implementation must maintain (though not necessarily directly export) an
enumerated errno to allow SLURM to discover
as practically as possible the reason for any failed API call. Plugin-specific enumerated
integer values should be used when appropriate. It is desirable that these values
be mapped into the range ESLURM_SCHED_MIN and ESLURM_SCHED_MAX
as defined in slurm/slurm_errno.h.
The error number should be returned by the function
slurm_sched_get_errno()
and string describing the error's meaning should be returned by the function
slurm_sched_strerror()
described below.
These values must not be used as return values in integer-valued functions
in the API. The proper error return value from integer-valued functions is SLURM_ERROR.
The implementation should endeavor to provide useful and pertinent information by
whatever means is practical. In some cases this means an errno for each credential,
since plugins must be re-entrant. If a plugin maintains a global errno in place of or in
addition to a per-credential errno, it is not required to enforce mutual exclusion on it.
Successful API calls are not required to reset any errno to a known value. However,
the initial value of any errno, prior to any error condition arising, should be
SLURM_SUCCESS.
API Functions
The following functions must appear. Functions which are not implemented should
be stubbed.
int slurm_sched_plugin_schedule (void);
Description: For passive schedulers, invoke a scheduling pass.
Arguments: None
Returns: SLURM_SUCCESS if successful. On failure,
the plugin should return SLURM_ERROR and set the errno to an appropriate value
to indicate the reason for failure.
uint32_t slurm_sched_plugin_initial_priority (uint32_t max_prio);
Description: Establish the initial priority of a new job.
Arguments: max_prio
(input) maximum priority of any previously submitted job. This can be used to
provide First-In-First-Out scheduling by assigning the new job a priority lower than this value.
This could also be used to establish an initial priority of zero for all jobs, representing a
"held" state. The scheduler plugin can then decide where and when to initiate pending jobs
by altering their priority and (optionally) list of required nodes.
Returns: The priority to be assigned to this job.
void slurm_sched_plugin_job_is_pending (void);
Description: Note that some job is pending execution..
Arguments: None
Returns: Nothing.
int slurm_sched_get_errno (void);
Description: Return the number of a scheduler
specific error.
Arguments: None
Returns: Error number for the last failure encountered by
the scheduler plugin.
const char *slurm_sched_strerror(int errnum);
Description: Return a string description of a scheduler
specific error code.
Arguments:
errnum (input) a scheduler
specific error code.
Returns: Pointer to string describing the error
or NULL if no description found in this plugin.
Versioning
This document describes version 0 of the SLURM Scheduler API. Future
releases of SLURM may revise this API. A scheduler plugin conveys its ability
to implement a particular API version using the mechanism outlined for SLURM plugins.
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