Expand cray gang scheduling documentation

Describe alps.conf changes required for gang scheduling on a cray system

doc/html/cray.shtml

@@ -500,9 +500,34 @@ for default and/or maximum memory limits (e.g. <b>DefMemPerNode</b> and
 <b>SelectTypeParameters=CR_Memory</b>), set an appropriate multi-programming
 level in each partition (e.g. <b>Shared=FORCE:2</b>), and enable gang
 scheduling (e.g. <b>PreemptMode=GANG</b>).</p>
+<pre>
+# Excerpt of slurm.conf
+DefMemPerNode=1000
+MaxMemPerNode=1000
+SelectType=select/cray
+SelectTypeParameters=CR_Memeory
+FrontEndName=frontend[00-03]
+NodeName=nid[00000-00511] Memory=4000 CPUs=6
+PartitionName=batch Nodes=nid[00000-00511] Shared=FORCE:4
+</pre>
+
+<p>ALPS' configuration file, <i>alps.conf</i>, also requires some modifcations
+in order to support gang scheduling. A sample configuration is shown below.
+Of particular note, <b>slice</b> is the time slice interval and should be set
+equal to zero in order for an entity external to ALPS (i.e. SLURM) to control
+when jobs are suspended and resumed. <b>loadLimit</b> indicates the maximum
+number of jobs per node and should be set to 2 for a Gemini interconnect and
+up to 4 otherwise.</p>
+<pre>
+# Excerpt of alps.conf
+nodeShare  share  # over-subscribe nodes
+sliceArch  xt
+slice      0
+loadLimit  4      # set to 2 for Gemini
+</pre>
 
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-<p style="text-align:center;">Last modified 24 June 2011</p></td>
+<p style="text-align:center;">Last modified 27 June 2011</p></td>
 
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