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Overview:

The objective of  PP-325 - Getting issue details... STATUS is to provide a hook that restricts resource availability for job processes by utilizing the Linux cgroup infrastructure. An introductory video to cgroups together with links to other resources may be found here: https://sysadmincasts.com/episodes/14-introduction-to-linux-control-groups-cgroups The definitive Linux kernel cgroup documentation may be found here: https://www.kernel.org/doc/Documentation/cgroup-v1/ It is assumed that the reader is familiar with the various cgroup subsystems and how they may be utilized. When the cgroup hook is enabled, it runs on every node assigned to the job that supports cgroups. When a job is started, the hook creates a set of directories for the configured subsystems based on the resource requirements of the job and then places the job process within the cgroup. The kernel then enforces resource restrictions based on the newly created cgroup settings while the job is running. The cgroup hook may be configured to periodically poll the job's cgroup while the job is running and updates resource utilization. When the job completes, the final resource utilization measurement is taken and the hook removes the cgroup directories it created when the job was initialized.

Interface 1: cgroup configuration file

  • Visibility: Public
  • Change Control: Experimental
  • Synopsis: JSON hook config file

  • Details: The configuration file allows the administrator to adjust the behavior of the cgroup hook across their cluster. The file must conform to JSON syntax. A sample configuration file is displayed and described below:
Example Cgroup Configuration File
{
    "cgroup_prefix"         : "pbspro",
    "exclude_hosts"         : ["node001", "node002"],
    "exclude_vntypes"       : ["disable_cgroups", "login_node"],
    "run_only_on_hosts"     : [],
    "periodic_resc_update"  : true,
    "vnode_per_numa_node"   : false,
    "online_offlined_nodes" : true,
    "use_hyperthreads"      : false,
    "cgroup" : {
        "cpuacct" : {
            "enabled"         : true,
            "exclude_hosts"   : ["node003"],
            "exclude_vntypes" : ["red_node"]
        },
        "cpuset" : {
            "enabled"         : true,
            "exclude_hosts"   : ["node004"],
            "exclude_vntypes" : ["green_node"]
        },
        "devices" : {
            "enabled"         : false,
            "exclude_hosts"   : [],
            "exclude_vntypes" : [],
            "allow"           : [
                "b *:* rwm",
                "c *:* rwm",
                ["mic/scif", "rwm"],
                ["nvidiactl", "rwm", "*"],
                ["nvidia-uvm", "rwm"]
            ]
        },
        "hugetlb" : {
            "enabled"         : false,
            "exclude_hosts"   : [],
            "exclude_vntypes" : [],
            "default"         : "0MB",
            "reserve_percent" : "0",
            "reserve_amount"  : "0MB"
        },
        "memory" : {
            "enabled"         : true,
            "exclude_hosts"   : [],
            "exclude_vntypes" : ["blue_node"],
            "soft_limit"      : false,
            "default"         : "256MB",
            "reserve_percent" : "0",
            "reserve_amount"  : "1GB"
        },
        "memsw" : {
            "enabled"         : true,
            "exclude_hosts"   : [],
            "exclude_vntypes" : ["grey_node"],
            "default"         : "256MB",
            "reserve_percent" : "0",
            "reserve_amount"  : "1GB"
        }
    }
}

Global Parameters:

The global parameters are used to modify the behavior of the cgroup hook across all nodes in the PBS Pro complex. They are not specific to any cgroup subsystem.

Parameter NameDefault ValueDescription
cgroup_prefix"pbspro"The parent directory under each cgroup subsystem where job cgroups will be created. For example, if the memory subsystem is located at /sys/fs/cgroup/memory then the memory cgroup for job 123.foo would be found in the /sys/fs/cgroup/memory/pbspro/123.foo directory.
cgroup_lock_file"/var/spool/pbs/mom_priv/cgroups.lock"This file is used to ensure reads and writes of the PBS Professional cgroups are mutually exclusive. The filesystem must support file locking.
exclude_hosts[ ]Specifies the list of hosts for which the cgroups hook should be disabled.
exclude_vntypes[ ]Specifies a list of vnode types for which the cgroups hook should be disabled. This applies to the builtin vntype resource assigned to a node.
kill_timeout10Specifies the number of seconds the cgroup hook should spend while attempting to kill a process within a cgroup.
nvidia-smi/usr/bin/nvidia-smiThe location of the nvidia-smi command on nodes supporting NVIDIA GPU devices.
online_offlined_nodesfalseWhen the cgroup hook fails to kill all processes within a cgroup, it will offline the node to prevent oversubscribing resources. The cgroup hook will periodically attempt to cleanup these "orphaned" cgroups. When set to false, the administrator must manually online the node when the problem is resolved. When set to true, the hook will return the node to service automatically.
periodic_resc_updatefalseWhen set to true, the hook periodically polls the cgroups of a running job and updates the jobs resource usage for cput, mem, and vmem resources. When set to false, MoM periodically polls /proc to obtain resource usage data.
placement_type"load_balanced"When this parameter is set to "load_balanced" the cgroup hook will reorder the sockets of a multi-socket node in an effort to distribute load across them. Sockets with the fewest jobs assigned to them will be allocated first. When any value other than "load_balanced" is specified the sockets are allocated in their assigned numeric order.
run_only_on_hosts[ ]Specifies the list of hosts for which the cgroup hook should be enabled. If the list is not empty, it overrides the settings of exclude_hosts and exclude_vntypes.
use_hyperthreadsfalseWhen set to true, hyperthreads are treated as though they were physical cores. When false, hyperthreads are not counted as physical cores and are not added to the cpuset created for the job on each node, even when hyperthreading is enabled for the CPU.
vnode_per_numa_nodefalseWhen set to true, each NUMA node will appear as though it were an independent vnode managed by a parent vnode. The parent vnode will have no resources associated with it. The vnode names will consist of the node name followed by an ordinal in brackets (e.g. foo[0], foo[1], foo[2], etc.). When set to false, the node will appear as a single vnode.

cpuacct Subsystem:

The cpuacct subsystem provides support for measuring CPU usage within a cgroup.

Parameter NameDefault ValueDescription
enabledfalseWhen set to true, the hook will update job CPU time using the value from the cpuacct subsystem (e.g. /sys/fs/cgroup/cpuacct/pbspro/123.foo/cpuacct.usage). When set to false, CPU time is accumulated when MoM periodically polls the processes of the job.
exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.

cpuset Subsystem:

The cpuset subsystem is used by the Linux kernel to restrict access to both CPU and memory based on available sockets and NUMA nodes.

Parameter NameDefault ValueDescription
enabledfalse

When set to true, the hook will create a cpuset for each job. The hook will configure the cpuset based on the resources requested by the job, taking into account the number of CPUs and memory requirements. This helps to ensure the job uses memory that is local to the CPUs assigned to the job. When set to false, the kernel is free to schedule processes and allocate memory based on the system configured policies.

NOTE: When running the SGI cpuset Mom this subsystem should be disabled to prevent interference with MoM's cpuset functionality. The administrator may also choose to run the standard Mom and enable this subsystem.

exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]

Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.

devices Subsystem:

The devices subsystem is used to grant or restrict access to devices on the system. This is most commonly used for accelerator cards such as GPUs, and MICs.

Parameter NameDefault ValueDescription
enabledfalseWhen set to true, the hook will configure the devices subsystem based on the number of nmics and ngpus requested by the job. Refer to the allow parameter below for additional information. When set to false, no cgroup will be created for the device subsystem.
exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]

Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.

allow[ ]

Specifies how access to devices will be controlled. The list consists of entries in one of the following formats:

  • A string entry will be used verbatim. For example, "b *:* rwm" allows full access (read, write, and mknod) to all block devices and "c *:* rwm" allows full access to all character devices.

  • A list containing two strings. For example, ["mic/scif","rwm"] will look for the major and minor number of the mic/scif device and allow full access. If /dev/mic reported "crw-rw-rw- 1 root root 244, 1 Mar 30 14:50 scif" then the line added to the allow file would look like "c 244:1 rwm"
  • A list containing three strings. For example, ["nvidiactl","rwm", "*"] will look for the major number of the nvidiactl device and allow full access. If /dev/nvidiactl reported "crw-rw-rw- 1 root root 284, 1 Mar 30 14:50 nvidiactl" then the line added to the allow file would look like "c 284:* rwm"

hugetlb Subsystem:

The hugetlb subsystem restricts the amount of huge page memory that may be used in a cgroup.

Parameter NameDefault ValueDescription
enabledfalseWhen set to true, the hook will register a limit that restricts the amount of huge page memory processes may access. When set to false, no limit is registered.
exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.
default0MBThe amount of huge page memory assigned to the cgroup when the job does not request hpmem.
reserve_percent0The percentage of available huge page memory that is not to be assigned to jobs. This will alter the amount of hpmem that MoM reports to the server. This value is then added to reserve_amount to obtain the total amount reserved.
reserve_amount0MBThe amount of available huge page memory that is not to be assigned to jobs. This will alter the amount of hpmem that MoM reports to the server. This is added to reserve_percent to obtain the total amount reserved.

memory Subsystem:

The memory subsystem restricts the amount of physical memory all of the processes in a cgroup may allocate. It works in conjunction with the memsw (memory and swap) subsystem to limit both physical memory and virtual memory. The memsw subsystem should be enabled if the memory subsystem is enabled. Otherwise, the virtual memory limit will remain unrestricted. If the processes in a cgroup exceed their physical memory limit, the kernel will begin to utilize swap space even if the node has sufficient physical memory to allocate. When a job specifies a mem limit without a vmem limit, the vmem limit is automatically set to the mem limit.

Parameter NameDefault ValueDescription
enabledfalseThe hook will register the physical memory limit for a job when set to true. No limit is registered when set to false.
exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.
soft_limitfalseA soft memory limit is used to specify the minimum amount of physical memory a job should be allocated before utilizing swap space. This adjusts the behavior of the kernel by allowing the physical memory allocation to exceed the amount specified in the soft limit when memory demand (a.k.a memory pressure) is low. The cgroup is ultimately limited to the amount of virtual memory specified in the memsw system. When memory pressure increases, the kernel will begin to page physical memory out to swap space until the soft limit is reached. Soft memory limits allow processes to take advantage of physical memory when it is available, but may lead to longer run times when memory pressure is high. Soft memory limits are used when this parameter is set to true. When set to false, hard memory limits are used that prevent the processes from ever exceeding their specified mem limit.
default0MBThe amount of physical memory available to a cgroup when no mem limit has been specified.
reserve_percent0The percentage of available physical memory that is not to be assigned to jobs. This will alter the amount of mem that MoM reports to the server. This value is then added to reserve_amount to obtain the total amount reserved.
reserve_amount0MBThe amount of available physical memory that is not to be assigned to jobs. This will alter the amount of mem that MoM reports to the server. This is added to reserve_percent to obtain the total amount reserved.

memsw Subsystem:

The memsw subsystem restricts the amount of virtual memory all of the processes in a cgroup may allocate. This includes both physical memory and swap space. The vmem resource may be used to specify the virtual memory limit. The value should always be greater than or equal to the amount of mem requested. The vmem resource must be added to the resources line in the sched_config file in order to schedule jobs based on virtual memory.

Parameter NameDefault ValueDescription
enabledfalseThe hook will register the virtual memory limit for a job when set to true. No limit is registered when set to false.
exclude_hosts[ ]Specifies the list of hosts for which the use of this subsystem should be disabled.
exclude_vntypes[ ]Specifies the list of vnode types for which the use of this subsystem should be disabled. This applies to the builtin vntype resource assigned to a node.
default0MBThe amount of virtual memory available to a cgroup when no vmem limit has been specified.
reserve_percent0The percentage of available virtual memory that is not to be assigned to jobs. This will alter the amount of vmem that MoM reports to the server. This value is then added to reserve_amount to obtain the total amount reserved.
reserve_amount0MBThe amount of available virtual memory that is not to be assigned to jobs. This will alter the amount of vmem that MoM reports to the server. This is added to reserve_percent to obtain the total amount reserved.


Interface 2: nmics

  • Visibility: Public
  • Change Control: Experimental
  • Synopsis: Integer resource used to request the number of Intel MIC devices required per chunk

  • Details: Users may submit jobs requesting nmics=<#> in order for the scheduler to assign nodes with a sufficient number of Intel MIC devices. The nmics resource must be added to the resources line in the scheduler configuration file for this resource to be considered for scheduling.

Interface 3: ngpus

  • Visibility: Public
  • Change Control: Experimental
  • Synopsis: Integer resource used to request the number of NVIDIA GPUs required per chunk

  • Details: Users may submit jobs requesting ngpus=<#> in order for the scheduler to assign nodes with a sufficient number of NVIDIA GPU devices. The ngpus resource must be added to the resources line in the scheduler configuration file for this resource to be considered for scheduling.

Interface 4: vmem

  • Visibility: Public
  • Change Control: Experimental
  • Synopsis: Size resource used to request the amount of virtual memory required per chunk

  • Details: Users may submit jobs requesting vmem=<size> in order for the scheduler to assign nodes with a sufficient amount of virtual memory. The vmem resource must be added to the resources line in the scheduler configuration file for this resource to be considered for scheduling. MoM must be restarted when the memsw subsystem is enabled before it will report a value for vmem.

Interface 5: hpmem

  • Visibility: Public
  • Change Control: Experimental
  • Synopsis: Size resource used to request the amount of huge page memory required per chunk

  • Details: Users may submit jobs requesting hpmem=<size> in order for the scheduler to assign nodes with a sufficient amount of huge page memory. The hpmem resource must be added to the resources line in the scheduler configuration file for this resource to be considered for scheduling. MoM must be restarted when the hugetlb subsystem is enabled before it will report a value for hpmem.

Administrator Notes

The cpuset MoM that is available for SGI systems utilizes libcpuset to manage cpusets for jobs. The cgroup hook provides similar functionality when the cpuset subsystem is enabled. Administrators should avoid using the cpuset MoM in conjuction with the cgroup hook.



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