Overhaul of the job scheduler. The new scheduler runs builds

synchronously instead of probabilistically scheduling jobs, which
means that the job load on a machine never exceeds a desired
threshold, and we can preferentially use faster machines when they are
available.  This has a dramatic effect on package build throughput,
although I don't yet have precise measurements of the performance
improvements.

Specifically, the changes are:

* Introduce the new variable maxjobs in portbuild.  This replaces the
build scheduling weights previously listed in the mlist file, which
now changes format to list the build machines only, ranked in order of
preference for job dispatches (i.e. faster machines first).

* The ${arch}/queue directory is used to list machines available for
jobs (file content is the number of jobs currently running on the
machine).  Changes to files in this directory are serialized using
lockf on the .lock file.

* Claim a machine with the getmachine script, with the .lock held.
This picks the machine with the fewestnumber of jobs running, which is
listed highest in the mlist file in case of multiple machines with
equal load.  The job counter is incremented, and the file removed if
the counter reaches ${maxjobs} for that machine.  If all machines are
busy, sleep for 15 seconds and retry.

* After we have claimed a machine, we run claim-chroot on it to claim
an empty chroot, as before.  If the claim fails, release the job from
the queue with the releasemachine script and retry after a 15 second
wait.

* When the build is finished, decrement the job counter with the
releasemachine script, with .lock held.

* The checkmachines script now exists only to poll the load averages
for admin convenience (every 2 minutes), and to ping for unreachable
machines.  When a machine cannot be reached, remove the entry in the
queue directory to stop further job dispatches to it.  This needs more
work to deal with reinitialization of machines after they become
available again.

4 files changed, 119 insertions, 29 deletions

diff --git a/Tools/portbuild/scripts/checkmachines b/Tools/portbuild/scripts/checkmachines
index 7f32bac93128..c6108d63b0a4 100755
--- a/Tools/portbuild/scripts/checkmachines
+++ b/Tools/portbuild/scripts/checkmachines
@@ -24,37 +24,12 @@ while true; do
   for i in ${arches}; do
     mlist=${buildroot}/${i}/mlist
   
-    unset DISPLAY
-  
-    min=99
     set $(cat $mlist)
-    while [ $# -gt 1 ]; do
+    while [ $# -gt 0 ]; do
       m=$1
-      l=$2
-      if (/usr/local/bin/nc -w 5 $m infoseek > ${buildroot}/${i}/loads/$m < /dev/null); then
-        num=$(awk '{print $1}' ${buildroot}/${i}/loads/$m)
-        if [ "x$num" = "x" ]; then
-  #	logger "checkmachines: file ${buildroot}/${i}/loads/$m is empty"
-  	  num=99
-        fi
-      else
-        # Don't ever want to list machines we couldn't connect to
-        num=999
-      fi
-
-      num=$(($num / $l))
-
-      if [ $num -lt $min ]; then
-        mach=$m
-        min=$num
-      elif [ $num = $min ]; then
-        mach="$mach $m"
-      fi
-
-      shift 2
-
+      lockf ${buildroot}/${i}/queue/.lock ${buildroot}/scripts/pollmachine ${i} ${m}
+      shift 1
     done
-    echo "$mach" > ${buildroot}/${i}/ulist
-
   done
+  sleep 120
 done
diff --git a/Tools/portbuild/scripts/getmachine b/Tools/portbuild/scripts/getmachine
new file mode 100755
index 000000000000..849d300e6270
--- /dev/null
+++ b/Tools/portbuild/scripts/getmachine
@@ -0,0 +1,53 @@
+#!/bin/sh
+#
+# Choose the least-loaded machine in the queue dir
+# Called with lock held
+# We know that everything in this directory has space for another job
+
+pb=$1
+arch=$2
+branch=$3
+
+qdir=${pb}/${arch}/queue
+
+cd $qdir
+set *
+if [ "$1" = "*" ]; then
+  echo ""
+  exit 1
+fi
+
+min=9999
+while [ $# -gt 0 ]; do
+  m=$1
+  num=$(cat $m)
+  if [ $num -lt $min ]; then
+    mach=$m
+    min=$num
+  elif [ $num -eq $min ]; then
+    mach="${mach} ${m}"
+  fi
+  shift
+done
+
+if [ "$min" = 9999 -o -z "${mach}" ]; then
+  echo ""
+  exit 1
+fi
+
+# Choose highest-priority machine that is free
+mach=$(echo ${mach} | tr -s ' ' '\n' | grep -F -f - ${pb}/${arch}/mlist | head -1)
+
+. ${pb}/${arch}/portbuild.conf
+test -f ${pb}/${arch}/portbuild.${mach} && . ${pb}/${arch}/portbuild.${mach}
+
+# Now that we've found a machine, register our claim in the queue
+if [ "$((${min}+1))" -ge "${maxjobs}" ]; then
+  rm ${mach}
+else
+  echo $(($min+1)) > ${mach}
+fi
+
+# Report to caller
+echo ${mach}
+exit 0
diff --git a/Tools/portbuild/scripts/pollmachine b/Tools/portbuild/scripts/pollmachine
new file mode 100755
index 000000000000..75cd9885ddee
--- /dev/null
+++ b/Tools/portbuild/scripts/pollmachine
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+buildroot=/var/portbuild
+
+i=$1
+m=$2
+if [ "$3" = "-queue" ]; then
+  queue=1
+else
+  queue=0
+fi
+
+infoseek_host=$m
+infoseek_port=infoseek
+. ${buildroot}/${i}/portbuild.conf
+if [ -f ${buildroot}/${i}/portbuild.${m} ]; then
+  . ${buildroot}/${i}/portbuild.${m}
+fi
+if (/usr/local/bin/nc -w 5 ${infoseek_host} ${infoseek_port} > ${buildroot}/${i}/loads/$m < /dev/null); then
+  if [ "${queue}" = 1 ]; then
+    num=$(awk '{print $1}' ${buildroot}/${i}/loads/$m)
+    if [ "$num" -lt "${maxjobs}" ]; then
+      echo ${num} > ${buildroot}/${i}/queue/$m
+      chown ports-${i} ${buildroot}/${i}/queue/$m
+    else
+      rm -f ${buildroot}/${i}/queue/$m
+    fi
+  fi
+else
+    rm -f ${buildroot}/${i}/queue/$m
+    exit 1
+fi
+exit 0
diff --git a/Tools/portbuild/scripts/releasemachine b/Tools/portbuild/scripts/releasemachine
new file mode 100755
index 000000000000..66d23b193845
--- /dev/null
+++ b/Tools/portbuild/scripts/releasemachine
@@ -0,0 +1,29 @@
+#!/bin/sh
+
+buildroot=/var/portbuild
+
+i=$1
+m=$2
+
+infoseek_host=$m
+infoseek_port=infoseek
+. ${buildroot}/${i}/portbuild.conf
+if [ -f ${buildroot}/${i}/portbuild.${m} ]; then
+  . ${buildroot}/${i}/portbuild.${m}
+fi
+
+q=${buildroot}/${i}/queue/$m
+if [ -f ${q} ]; then
+  num=$(cat $q)
+else
+  num=${maxjobs}
+fi
+
+if [ "$num" -gt 0 ]; then
+  echo $((${num}-1)) > $q
+else
+  echo 0 > $q
+fi
+
+chown ports-${i} ${q}
+exit 0