<!--#include virtual="header.txt"-->

<h1>Support for Multi-core/Multi-thread Architectures</h1>

<h2 id="contents">Contents<a class="slurm_link" href="#contents"></a></h2>
<UL>
<LI> <a href=#defs>Definitions</a>
<LI> <a href=#flags>Overview of srun flags</a>
<LI> <a href=#motivation>Motivation behind high-level srun flags</a>
<LI> <a href=#utilities>Extensions to sinfo/squeue/scontrol</a>
<LI> <a href=#config>Configuration settings in slurm.conf</a>
</UL>

<h2 id="defs">Definitions<a class="slurm_link" href="#defs"></a></h2>

<dl>
<dt><b>BaseBoard</b>
<dd>Also called motherboard.
<dt><b>LDom</b>
<dd>Locality domain or NUMA domain. May be equivalent to BaseBoard or Socket.
<dt><b>Socket/Core/Thread</b>
<dd>Figure 1 illustrates the notion of Socket, Core and Thread as it is defined
in Slurm's multi-core/multi-thread support documentation.
<dt><b>CPU</b>
<dd>Depending upon system configuration, this can be either a core or a thread.
</dl>

<center>
<img src="mc_support.gif">
<br>
Figure 1: Definitions of Socket, Core, & Thread
</center>

<dl>
<dt><b>Affinity</b>
<dd>The state of being bound to a specific logical processor.
<dt><b>Affinity Mask</b>
<dd>A bitmask where indices correspond to logical processors.
The least significant bit corresponds to the first
logical processor number on the system, while the most
significant bit corresponds to the last logical processor
number on the system.
A '1' in a given position indicates a process can run
on the associated logical processor.
<dt><b>Fat Masks</b>
<dd>Affinity masks with more than 1 bit set
allowing a process to run on more than one logical processor.
</dl>

<h2 id="flags">Overview of srun flags
<a class="slurm_link" href="#flags"></a>
</h2>

<p>Many flags have been defined to allow users to
better take advantage of this architecture by
explicitly specifying the number of sockets, cores, and threads required
by their application.  Table 1 summarizes these options.

<P>
<table border=1 cellspacing=0 cellpadding=4>
<tr><td colspan=2>
<b><a href="#srun_lowlevelmc">Low-level (explicit binding)</a></b>
</td></tr>
<tr>
    <td> --cpu-bind=... </td>
    <td>Explicit process affinity binding and control options
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_highlevelmc">High-level (automatic mask generation)</a></b>
</td></tr>
<tr>
    <td> --sockets-per-node=<i>S</i></td>
    <td>Number of sockets in a node to dedicate to a job (minimum)
</td></tr>
<tr>
    <td> --cores-per-socket=<i>C</i></td>
    <td> Number of cores in a socket to dedicate to a job (minimum)
</td></tr>
<tr>
    <td> --threads-per-core=<i>T</i></td>
    <td> Minimum number of threads in a core to dedicate to a job. In task
	 layout, use the specified maximum number of threads per-core.
</td></tr>
<tr>
    <td> -B <i>S[:C[:T]]</i></td>
    <td> Combined shortcut option for --sockets-per-node, --cores-per_cpu, --threads-per_core
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_dist">Task Distribution Options</b>
</td></tr>
<tr>
    <td> -m / --distribution </td>
    <td> Distributions of: arbitrary | block | cyclic
    		| <a href="dist_plane.html"><u>plane=<i>x</i></u></a>
		| <u>[block|cyclic]:[block|cyclic|fcyclic]</u>
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_consres">Memory as a consumable resource</a></b>
</td></tr>
<tr>
    <td> --mem=<i>mem</i></td>
    <td> amount of real memory per node required by the job.
</td></tr>
<tr>
    <td> --mem-per-cpu=<i>mem</i></td>
    <td> amount of real memory per allocated CPU required by the job.
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_ntasks">Task invocation control</a></b>
</td></tr>
<tr>
    <td> --cpus-per-task=<i>CPUs</i></td>
    <td> number of CPUs required per task
</td></tr>
    <td> --ntasks-per-node=<i>ntasks</i></td>
    <td> number of tasks to invoke on each node
</td></tr>
    <td> --ntasks-per-socket=<i>ntasks</i></td>
    <td> number of tasks to invoke on each socket
</td></tr>
    <td> --ntasks-per-core=<i>ntasks</i></td>
    <td> number of tasks to invoke on each core
</td></tr>
    <td> --overcommit</td>
    <td> Permit more than one task per CPU
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_hints">Application hints</a></b>
</td></tr>
<tr>
    <td> --hint=compute_bound</td>
    <td> use all cores in each socket
</td></tr>
    <td> --hint=memory_bound</td>
    <td> use only one core in each socket
</td></tr>
    <td> --hint=[no]multithread</td>
    <td> [don't] use extra threads with in-core multi-threading
</td></tr>
<tr><td colspan=2>
<b><a href="#srun_hints">Resources reserved for system use</a></b>
</td></tr>
<tr>
    <td> --core-spec=<i>cores</i></td>
    <td> Count of cores to reserve for system use
</td></tr>
    <td> --thread-spec=<i>threads</i></td>
    <td> Count of threads to reserve for system use
</td></tr>
</table>

<p>
<center>
Table 1: srun flags to support the multi-core/multi-threaded environment
</center>

<p>It is important to note that many of these flags are only meaningful if the
processes have some affinity to specific CPUs and (optionally) memory.
Inconsistent options generally result in errors.
Task affinity is configured using the TaskPlugin parameter in the slurm.conf file.
Several options exist for the TaskPlugin depending upon system architecture
and available software, any of them except "task/none" will bind tasks to CPUs.
See the "Task Launch" section if generating slurm.conf via
<a href="configurator.html">configurator.html</a>.</p>

<h3 id="srun_lowlevelmc">Low-level --cpu-bind=... - Explicit binding interface
<a class="slurm_link" href="#srun_lowlevelmc"></a>
</h3>

<p>The following srun flag provides a low-level core binding interface:</p>


<PRE>
--cpu-bind=        Bind tasks to CPUs
    q[uiet]         quietly bind before task runs (default)
    v[erbose]       verbosely report binding before task runs
    no[ne]          don't bind tasks to CPUs (default)
    rank            bind by task rank
    map_cpu:<i>&lt;list&gt;</i>  specify a CPU ID binding for each task
                    where <i>&lt;list&gt;</i> is
                    <i>&lt;cpuid1&gt;,&lt;cpuid2&gt;,...&lt;cpuidN&gt;</i>
    mask_cpu:<i>&lt;list&gt;</i> specify a CPU ID binding mask for each
                    task where <i>&lt;list&gt;</i> is
                    <i>&lt;mask1&gt;,&lt;mask2&gt;,...&lt;maskN&gt;</i>
    rank_ldom       bind task by rank to CPUs in a NUMA
                    locality domain
    map_ldom:<i>&lt;list&gt;</i> specify a NUMA locality domain ID
                    for each task where <i>&lt;list&gt;</i> is
                    <i>&lt;ldom1&gt;,&lt;ldom2&gt;,...&lt;ldomN&gt;</i>
    rank_ldom       bind task by rank to CPUs in a NUMA
                    locality domain where <i>&lt;list&gt;</i> is
                    <i>&lt;ldom1&gt;,&lt;ldom2&gt;,...&lt;ldomN&gt;</i>
    mask_ldom:<i>&lt;list&gt;</i> specify a NUMA locality domain ID mask
                    for each task where <i>&lt;list&gt;</i> is
                    <i>&lt;ldom1&gt;,&lt;ldom2&gt;,...&lt;ldomN&gt;</i>
    ldoms           auto-generated masks bind to NUMA locality
                    domains
    sockets         auto-generated masks bind to sockets
    cores           auto-generated masks bind to cores
    threads         auto-generated masks bind to threads
    help            show this help message
</PRE>

<p> The affinity can be either set to either a specific logical processor
(socket, core, threads) or at a coarser granularity than the lowest level
of logical processor (core or thread).
In the later case the processes are allowed to utilize multiple processors
within a specific socket or core.

<p>Examples:</p>

<UL>
<UL>
<LI> srun -n 8 -N 4 --cpu-bind=mask_cpu:0x1,0x4 a.out
<LI> srun -n 8 -N 4 --cpu-bind=mask_cpu:0x3,0xD a.out
</UL>
</UL>

<p>See also 'srun --cpu-bind=help' and 'man srun'</p>

<h3 id="srun_highlevelmc">
High-level -B <i>S[:C[:T]]</i> - Automatic mask generation interface
<a class="slurm_link" href="#srun_highlevelmc"></a>
</h3>

<p>We have updated the node
selection infrastructure with a mechanism that allows selection of logical
processors at a finer granularity. Users are able to request a specific number
of nodes, sockets,&nbsp; cores, and threads:</p>

<PRE>
-B, --extra-node-info=<i>S[:C[:T]]</i>            Expands to:
  --sockets-per-node=<i>S</i>   number of sockets per node to allocate
  --cores-per-socket=<i>C</i>   number of cores per socket to allocate
  --threads-per-core=<i>T</i>   number of threads per core to allocate
                each field can be 'min' or wildcard '*'

     <font face="serif">Total cpus requested = (<i>Nodes</i>) x (<i>S</i> x <i>C</i> x <i>T</i>)</font>
</PRE>

<p>Examples:

<UL>
<UL>
<LI> srun -n 8 -N 4 -B 2:1 a.out
<LI> srun -n 8 -N 4 -B 2   a.out
<BR>
note: compare the above with the previous corresponding --cpu-bind=... examples

<LI> srun -n 16 -N 4 a.out
<LI> srun -n 16 -N 4 -B 2:2:1 a.out
<LI> srun -n 16 -N 4 -B 2:2:1 a.out
<BR> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;or
<LI> srun -n 16 -N 4 --sockets-per-node=2 --cores-per-socket=2 --threads-per-core=1 a.out
<LI> srun -n 16 -N 2-4 -B '1:*:1' a.out
<LI> srun -n 16 -N 4-2 -B '2:*:1' a.out
<LI> srun -n 16 -N 4-4 -B '1:1' a.out
</UL>
</UL>

<p>Notes:</p>
<ul>
 <li> Adding --cpu-bind=no to the command line will cause the processes
      to not be bound the logical processors.
 <li> Adding --cpu-bind=verbose to the command line (or setting the
      CPU_BIND environment variable to "verbose") will cause each task
      to report the affinity mask in use
 <li> Binding is on by default when -B is used. The default binding on
      multi-core/multi-threaded systems is equivalent to the level of
      resource enumerated in the -B option.
</ul>

<p>See also 'srun --help' and 'man srun'</p>

<h3 id="srun_dist">Task distribution options: Extensions to -m / --distribution
<a class="slurm_link" href="#srun_dist"></a>
</h3>

<p>The -m / --distribution option for distributing processes across nodes
has been extended to also describe the distribution within the lowest level
of logical processors.
Available distributions include:
<br>
arbitrary | block | cyclic | <u>plane=<i>x</i></u> | <u>[block|cyclic]:[block|cyclic|fcyclic]</u>
</p>

<p>The  <A HREF="dist_plane.html">plane distribution</A> (plane=<i>x</i>)
results in a block:cyclic distribution of blocksize equal to <i>x</i>.
In the following we use "lowest level of logical processors"
to describe sockets, cores or threads depending of the architecture.
The distribution divides
the cluster into planes (including a number of the lowest level of logical
processors on each node) and then schedule first within each plane and then
across planes.</p>

<p>For the two dimensional distributions ([block|cyclic]:[block|cyclic|fcyclic]),
the second distribution (after ":") allows users to specify a distribution
method for processes within a node and applies to the lowest level of logical
processors (sockets, core or thread depending on the architecture).
When a task requires more than one CPU, the <i>cyclic</i> will allocate all
of those CPUs as a group (i.e. within the same socket if possible) while 
<i>fcyclic</i> would distribute each of those CPU of the in a cyclic fashion
across sockets.</p>

<p>The binding is enabled automatically when high level flags are used as long
as the task/affinity plug-in is enabled. To disable binding at the job level
use --cpu-bind=no.</p>

<p>The distribution flags can be combined with the other switches:

<UL>
<UL>
<LI>srun -n 16 -N 4 -B '2:*:1' -m block:cyclic --cpu-bind=socket a.out
<LI>srun -n 16 -N 4 -B '2:*:1' -m plane=2 --cpu-bind=core a.out
<LI>srun -n 16 -N 4 -B '2:*:1' -m plane=2 a.out
</UL>
</UL>

<p>The default distribution on multi-core/multi-threaded systems is equivalent
to -m block:cyclic with --cpu-bind=thread.</p>

<p>See also 'srun --help'</p>

<h3 id="srun_consres">Memory as a Consumable Resource
<a class="slurm_link" href="#srun_consres"></a>
</h3>

<p>The --mem flag specifies the maximum amount of memory in MB
needed by the job per node.  This flag is used to support the memory
as a consumable resource allocation strategy.</p>

<PRE>
--mem=<i>MB</i>      maximum amount of real memory per node
              required by the job.
</PRE>

<p>This flag allows the scheduler to co-allocate jobs on specific nodes
given that their added memory requirement do not exceed the total amount
of memory on the nodes.</p>


<p>In order to use memory as a consumable resource, the select/cons_tres
plugin must be first enabled in slurm.conf:
<PRE>
SelectType=select/cons_tres     # enable consumable resources
SelectTypeParameters=CR_Memory  # memory as a consumable resource
</PRE>

<p> Using memory as a consumable resource is typically combined with
the CPU, Socket, or Core consumable resources using SelectTypeParameters
values of: CR_CPU_Memory, CR_Socket_Memory or CR_Core_Memory

<p>See the "Resource Selection" section if generating slurm.conf
via <a href="configurator.html">configurator.html</a>.

<p>See also 'srun --help' and 'man srun'</p>

<h3 id="srun_ntasks">Task invocation as a function of logical processors
<a class="slurm_link" href="#srun_ntasks"></a>
</h3>

<p>The <tt>--ntasks-per-{node,socket,core}=<i>ntasks</i></tt> flags
allow the user to request that no more than <tt><i>ntasks</i></tt>
be invoked on each node, socket, or core.
This is similar to using <tt>--cpus-per-task=<i>ncpus</i></tt>
but does not require knowledge of the actual number of cpus on
each node.  In some cases, it is more convenient to be able to
request that no more than a specific number of ntasks be invoked
on each node, socket, or core.  Examples of this include submitting
an app where only one "task/rank" should be
assigned to each node while allowing the job to utilize
all of the parallelism present in the node, or submitting a single
setup/cleanup/monitoring job to each node of a pre-existing
allocation as one step in a larger job script.
This can now be specified via the following flags:</p>

<PRE>
--ntasks-per-node=<i>n</i>    number of tasks to invoke on each node
--ntasks-per-socket=<i>n</i>  number of tasks to invoke on each socket
--ntasks-per-core=<i>n</i>    number of tasks to invoke on each core
</PRE>

<p>For example, given a cluster with nodes containing two sockets,
each containing two cores, the following commands illustrate the
behavior of these flags:</p>
<pre>
% srun -n 4 hostname
hydra12
hydra12
hydra12
hydra12
% srun -n 4 --ntasks-per-node=1 hostname
hydra12
hydra13
hydra14
hydra15
% srun -n 4 --ntasks-per-node=2 hostname
hydra12
hydra12
hydra13
hydra13
% srun -n 4 --ntasks-per-socket=1 hostname
hydra12
hydra12
hydra13
hydra13
% srun -n 4 --ntasks-per-core=1 hostname
hydra12
hydra12
hydra12
hydra12
</pre>

<p>See also 'srun --help' and 'man srun'</p>

<h3 id="srun_hints">Application hints
<a class="slurm_link" href="#srun_hints"></a>
</h3>

<p>Different applications will have various levels of resource
requirements. Some applications tend to be computationally intensive
but require little to no inter-process communication. Some applications
will be memory bound, saturating the memory bandwidth of a processor
before exhausting the computational capabilities. Other applications
will be highly communication intensive causing processes to block
awaiting messages from other processes. Applications with these
different properties tend to run well on a multi-core system given
the right mappings.</p>

<p>For computationally intensive applications, all cores in a multi-core
system would normally be used. For memory bound applications, only
using a single core on each socket will result in the highest per
core memory bandwidth. For communication intensive applications,
using in-core multi-threading (e.g. hyperthreading, SMT, or TMT)
may also improve performance.
The following command line flags can be used to communicate these
types of application hints to the Slurm multi-core support:</p>

<PRE>
--hint=             Bind tasks according to application hints
    compute_bound   use all cores in each socket
    memory_bound    use only one core in each socket
    [no]multithread [don't] use extra threads with in-core multi-threading
    help            show this help message
</PRE>

<p>For example, given a cluster with nodes containing two sockets,
each containing two cores, the following commands illustrate the
behavior of these flags.  In the verbose --cpu-bind output, tasks
are described as 'hostname, task Global_ID Local_ID [PID]':</p>
<pre>
% srun -n 4 --hint=compute_bound --cpu-bind=verbose sleep 1
cpu-bind=MASK - hydra12, task  0  0 [15425]: mask 0x1 set
cpu-bind=MASK - hydra12, task  1  1 [15426]: mask 0x4 set
cpu-bind=MASK - hydra12, task  2  2 [15427]: mask 0x2 set
cpu-bind=MASK - hydra12, task  3  3 [15428]: mask 0x8 set

% srun -n 4 --hint=memory_bound --cpu-bind=verbose sleep 1
cpu-bind=MASK - hydra12, task  0  0 [15550]: mask 0x1 set
cpu-bind=MASK - hydra12, task  1  1 [15551]: mask 0x4 set
cpu-bind=MASK - <u><b>hydra13</b></u>, task  2  <u><b>0</b></u> [14974]: mask 0x1 set
cpu-bind=MASK - <u><b>hydra13</b></u>, task  3  <u><b>1</b></u> [14975]: mask 0x4 set
</pre>

<p>See also 'srun --hint=help' and 'man srun'</p>
<!-------------------------------------------------------------------------->
<h2 id="motivation">Motivation behind high-level srun flags
<a class="slurm_link" href="#motivation"></a>
</h2>

<p >The motivation behind allowing users to use higher level <i>srun</i>
flags instead of --cpu-bind is that the later can be difficult to use. The
proposed high-level flags are easier to use than --cpu-bind because:</p>

<ul>
<li>Affinity mask generation happens automatically when using the high-level flags. </li>
<li>The length and complexity of the --cpu-bind flag vs. the length
of the combination of -B and --distribution flags make the high-level
flags much easier to use.</li>
</ul>

<p>Also as illustrated in the example below it is much simpler to specify
a different layout using the high-level flags since users do not have to
recalculate mask or CPU IDs. This approach is much simpler than
rearranging the mask or map.</p>

<p>Given a 32-process job and a four node, dual-socket, dual-core
cluster, we want to use a block distribution across the four nodes and then a
cyclic distribution within the node across the physical processors. Below we
show how to obtain the wanted layout using 1) high-level flags and
2) --cpubind</p>

<h3 id="high_level">High-Level flags
<a class="slurm_link" href="#high_level"></a>
</h3>

<p>Using Slurm's high-level flag, users can obtain the above layout with
either of the following submissions since --distribution=block:cyclic
is the default distribution method.</p>

<pre>
$ srun -n 32 -N 4 -B 4:2 --distribution=block:cyclic a.out
</pre>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;or
<pre>
$ srun -n 32 -N 4 -B 4:2 a.out
</pre>

<p>The cores are shown as c0 and c1 and the processors are shown
as p0 through p3. The resulting task IDs are: </p>

<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0 </td><td align=center> 4 </td></tr>
<tr><td>p2</td><td align=center> 2 </td><td align=center> 6 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 1 </td><td align=center> 5 </td></tr>
<tr><td>p3</td><td align=center> 3 </td><td align=center> 7 </td></tr>
</table>
</td>
</tr>
</table>

<p>The computation and assignment of the task IDs is transparent
to the user. Users don't have to worry about the core numbering (Section
Pinning processes to cores) or any setting any CPU affinities. By default CPU affinity
will be set when using multi-core supporting flags. </p>

<h3 id="low_level">Low-level flag --cpu-bind
<a class="slurm_link" href="#low_level"></a>
</h3>

<p>Using Slurm's --cpu-bind flag, users must compute the CPU IDs or
masks as well as make sure they understand the core numbering on their
system. Another problem arises when core numbering is not the same on all
nodes. The --cpu-bind option only allows users to specify a single
mask for all the nodes. Using Slurm high-level flags remove this limitation
since Slurm will correctly generate the appropriate masks for each requested nodes.</p>

<h3 id="core_block">
On a four dual-socket dual-core node cluster with core block numbering
<a class="slurm_link" href="#core_block"></a>
</h3>

<p>The cores are shown as c0 and c1 and the processors are shown
as p0 through p3. The CPU IDs within a node in the block numbering are:
(this information is available from the /proc/cpuinfo file on the system)</p>

<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0 </td><td align=center> 1 </td></tr>
<tr><td>p2</td><td align=center> 4 </td><td align=center> 5 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 2 </td><td align=center> 3 </td></tr>
<tr><td>p3</td><td align=center> 6 </td><td align=center> 7 </td></tr>
</table>
</td>
</tr>
</table>

<p >&nbsp;resulting in the following mapping for processor/cores
and task IDs which users need to calculate: </p>

<center>
mapping for processors/cores
</center>
<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0x01 </td><td align=center> 0x02 </td></tr>
<tr><td>p2</td><td align=center> 0x10 </td><td align=center> 0x20 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 0x04 </td><td align=center> 0x08 </td></tr>
<tr><td>p3</td><td align=center> 0x40 </td><td align=center> 0x80 </td></tr>
</table>
</td>
</tr>
</table>

<p>
<center>
task IDs
</center>
<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0 </td><td align=center> 4 </td></tr>
<tr><td>p2</td><td align=center> 2 </td><td align=center> 6 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 1 </td><td align=center> 5 </td></tr>
<tr><td>p3</td><td align=center> 3 </td><td align=center> 7 </td></tr>
</table>
</td>
</tr>
</table>

<p>The above maps and task IDs can be translated into the
following command:</p>

<pre>
$ srun -n 32 -N 4 --cpu-bind=mask_cpu:1,4,10,40,2,8,20,80 a.out
</pre>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;or
<pre>
$ srun -n 32 -N 4 --cpu-bind=map_cpu:0,2,4,6,1,3,5,7 a.out
</pre>

<h3 id="core_cyclic">
Same cluster but with its core numbered cyclic instead of block
<a class="slurm_link" href="#core_cyclic"></a>
</h3>

<p>On a system with cyclically numbered cores, the correct mask
argument to the <i>srun</i> command looks like: (this will
achieve the same layout as the command above on a system with core block
numbering.)</p>

<pre>
$ srun -n 32 -N 4 --cpu-bind=map_cpu:0,1,2,3,4,5,6,7 a.out
</pre>

<h3 id="map_cpu">Block map_cpu on a system with cyclic core numbering
<a class="slurm_link" href="#map_cpu"></a>
</h3>

<p>If users do not check their system's core numbering before specifying
the map_cpu list and thereby do not realize that the system has cyclic core
numbering instead of block numbering then they will not get the expected
layout. For example, if they decide to re-use their command from above:</p>

<pre>
$ srun -n 32 -N 4 --cpu-bind=map_cpu:0,2,4,6,1,3,5,7 a.out
</pre>

<p>they get the following unintentional task ID layout:</p>

<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0 </td><td align=center> 2 </td></tr>
<tr><td>p2</td><td align=center> 1 </td><td align=center> 3 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 4 </td><td align=center> 6 </td></tr>
<tr><td>p3</td><td align=center> 5 </td><td align=center> 7 </td></tr>
</table>
</td>
</tr>
</table>

<p>since the processor IDs within a node in the cyclic numbering are:</p>

<table border=0 align=center>
<tr>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p0</td><td align=center> 0 </td><td align=center> 4 </td></tr>
<tr><td>p2</td><td align=center> 2 </td><td align=center> 6 </td></tr>
</table>
</td>
<td width=5>
</td>
<td>
<table border=1 align=center>
<tr><td>  </td>
<td width=40 align=center>c0</td><td width=40 align=center>c1</td></tr>
<tr><td>p1</td><td align=center> 1 </td><td align=center> 5 </td></tr>
<tr><td>p3</td><td align=center> 3 </td><td align=center> 7 </td></tr>
</table>
</td>
</tr>
</table>

<p>The important conclusion is that using the --cpu-bind flag is not
trivial and that it assumes that users are experts.</p>

<!-------------------------------------------------------------------------->
<h2 id="utilities">Extensions to sinfo/squeue/scontrol
<a class="slurm_link" href="#utilities"></a>
</h2>

<p>Several extensions have also been made to the other Slurm utilities to
make working with multi-core/multi-threaded systems easier.</p>

<!- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<h3 id="sinfo">sinfo<a class="slurm_link" href="#sinfo"></a></h3>

<p>The long version (-l) of the sinfo node listing (-N) has been
extended to display the sockets, cores, and threads present for each
node.  For example:

<PRE>
% sinfo -N
NODELIST     NODES PARTITION STATE
hydra[12-15]     4    parts* idle

% sinfo -lN
Thu Sep 14 17:47:13 2006
NODELIST     NODES PARTITION       STATE CPUS    S:C:T MEMORY TMP_DISK WEIGHT FEATURES REASON
hydra[12-15]     4    parts*        idle   8+ 2+:4+:1+   2007    41447      1   (null) none

% sinfo -lNe
Thu Sep 14 17:47:18 2006
NODELIST     NODES PARTITION       STATE CPUS    S:C:T MEMORY TMP_DISK WEIGHT FEATURES REASON

hydra[12-14]     3    parts*        idle    8    2:4:1   2007    41447      1   (null) none
hydra15          1    parts*        idle   64    8:4:2   2007    41447      1   (null) none
</PRE>

<p>For user specified output formats (-o/--format) and sorting (-S/--sort),
the following identifiers are available:</p>

<PRE>
%X  Number of sockets per node
%Y  Number of cores per socket
%Z  Number of threads per core
%z  Extended processor information: number of
    sockets, core, threads (S:C:T) per node
</PRE>

<p>For example:</p>

<PRE>
% sinfo -o '%9P %4c %8z %8X %8Y %8Z'
PARTITION CPUS S:C:T    SOCKETS  CORES    THREADS
parts*    4    2:2:1    2        2        1
</PRE>

<p>See also 'sinfo --help' and 'man sinfo'</p>

<!- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<h3 id="squeue">squeue<a class="slurm_link" href="#squeue"></a></h3>

<p>For user specified output formats (-o/--format) and sorting (-S/--sort),
the following identifiers are available:</p>

<PRE>
%m  Size of memory (in MB) requested by the job
%H  Number of requested sockets per node
%I  Number of requested cores per socket
%J  Number of requested threads per core
%z  Extended processor information: number of requested
    sockets, cores, threads (S:C:T) per node
</PRE>

<p>Below is an example squeue output after running 7 copies of:</p>

<UL>
<UL>
<DL>% srun -n 4 -B 2:2:1 --mem=1024 sleep 100 &
</UL>
</UL>

<PRE>
% squeue -o '%.5i %.2t %.4M %.5D %7H %6I %7J %6z %R'
JOBID ST TIME NODES SOCKETS CORES THREADS S:C:T NODELIST(REASON)
   17 PD 0:00     1 2       2     1       2:2:1 (Resources)
   18 PD 0:00     1 2       2     1       2:2:1 (Resources)
   19 PD 0:00     1 2       2     1       2:2:1 (Resources)
   13  R 1:27     1 2       2     1       2:2:1 hydra12
   14  R 1:26     1 2       2     1       2:2:1 hydra13
   15  R 1:26     1 2       2     1       2:2:1 hydra14
   16  R 1:26     1 2       2     1       2:2:1 hydra15
</PRE>

<p>The squeue command can also display the memory size of jobs, for example:</p>

<PRE>
% sbatch --mem=123 tmp
Submitted batch job 24

$ squeue -o "%.5i %.2t %.4M %.5D %m"
JOBID ST TIME NODES MIN_MEMORY
  24   R 0:05     1 123
</PRE>

<p>See also 'squeue --help' and 'man squeue'</p>

<!- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
<h3 id="scontrol">scontrol<a class="slurm_link" href="#scontrol"></a></h3>

<p>The following job settings can be adjusted using scontrol:

<PRE>
Requested Allocation:
  ReqSockets=&lt;count&gt;  Set the job's count of required sockets
  ReqCores=&lt;count&gt;    Set the job's count of required cores
  ReqThreads=&lt;count&gt;  Set the job's count of required threads
</PRE>

<p>For example:</p>

<PRE>
# scontrol update JobID=17 ReqThreads=2
# scontrol update JobID=18 ReqCores=4
# scontrol update JobID=19 ReqSockets=8

% squeue -o '%.5i %.2t %.4M %.5D %9c %7H %6I %8J'
JOBID ST TIME NODES MIN_PROCS SOCKETS CORES THREADS
   17 PD 0:00     1 1         4       2     1
   18 PD 0:00     1 1         8       4     2
   19 PD 0:00     1 1         4       2     1
   13  R 1:35     1 0         0       0     0
   14  R 1:34     1 0         0       0     0
   15  R 1:34     1 0         0       0     0
   16  R 1:34     1 0         0       0     0
</PRE>

<p>The 'scontrol show job' command can be used to display
the number of allocated CPUs per node as well as the socket, cores,
and threads specified in the request and constraints.

<PRE>
% srun -N 2 -B 2:1 sleep 100 &
% scontrol show job 20
JobId=20 UserId=(30352) GroupId=users(1051)
   Name=sleep
   Priority=4294901749 Partition=parts BatchFlag=0
   AllocNode:Sid=hydra16:3892 TimeLimit=UNLIMITED
   JobState=RUNNING StartTime=09/25-17:17:30 EndTime=NONE
   NodeList=hydra[12-14] NodeListIndices=0,2,-1
   <u>AllocCPUs=1,2,1</u>
   NumCPUs=4 ReqNodes=2 <u>ReqS:C:T=2:1:*</u>
   OverSubscribe=0 Contiguous=0 CPUs/task=0
   MinCPUs=0 MinMemory=0 MinTmpDisk=0 Features=(null)
   Dependency=0 Account=(null) Reason=None Network=(null)
   ReqNodeList=(null) ReqNodeListIndices=-1
   ExcNodeList=(null) ExcNodeListIndices=-1
   SubmitTime=09/25-17:17:30 SuspendTime=None PreSusTime=0
</PRE>

<p>See also 'scontrol --help' and 'man scontrol'</p>

<!-------------------------------------------------------------------------->
<h2 id="config">Configuration settings in slurm.conf
<a class="slurm_link" href="#config"></a>
</h2>

<p>Several slurm.conf settings are available to control the multi-core
features described above.

<p>In addition to the description below, also see the "Task Launch" and
"Resource Selection" sections if generating slurm.conf
via <a href="configurator.html">configurator.html</a>.

<p>As previously mentioned, in order for the affinity to be set, the
task/affinity plugin must be first enabled in slurm.conf:

<PRE>
TaskPlugin=task/affinity          # enable task affinity
</PRE>

<p>This setting is part of the task launch specific parameters:</p>

<PRE>
# o Define task launch specific parameters
#
#    "TaskProlog" : Define a program to be executed as the user before each
#                   task begins execution.
#    "TaskEpilog" : Define a program to be executed as the user after each
#                   task terminates.
#    "TaskPlugin" : Define a task launch plugin. This may be used to
#                   provide resource management within a node (e.g. pinning
#                   tasks to specific processors). Permissible values are:
#      "task/affinity" : CPU affinity support
#      "task/cgroup"   : bind tasks to resources using Linux cgroup
#      "task/none"     : no task launch actions, the default
#
# Example:
#
# TaskProlog=/usr/local/slurm/etc/task_prolog # default is none
# TaskEpilog=/usr/local/slurm/etc/task_epilog # default is none
# TaskPlugin=task/affinity                    # default is task/none
</PRE>

<p>Declare the node hardware configuration in slurm.conf:

<PRE>
NodeName=dualcore[01-16] CoresPerSocket=2 ThreadsPerCore=1
</PRE>

<p>For a more complete description of the various node configuration options
see the slurm.conf man page.</p>
<!-------------------------------------------------------------------------->
<p style="text-align:center;">Last modified 19 May 2023</p>

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