instruments: add proc_stat

Add an instrument that monitors CPU load using data from /proc/stat

wa/instruments/proc_stat/gather-load.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+BUSYBOX=$1
+OUTFILE=$2
+PERIOD=$3
+STOP_SIGNAL_FILE=$4
+
+if [ "$#" != "4" ]; then
+    echo "USAGE: gather-load.sh BUSYBOX OUTFILE PERIOD STOP_SIGNAL_FILE"
+    exit 1
+fi
+
+echo "timestamp,user,nice,system,idle,iowait,irq,softirq,steal,guest,guest_nice" > $OUTFILE
+while true; do
+    echo -n $(${BUSYBOX} date -Iseconds) >> $OUTFILE
+    ${BUSYBOX} cat /proc/stat | ${BUSYBOX} head -n 1 | \
+        ${BUSYBOX} cut -d ' ' -f 2- | ${BUSYBOX} sed 's/ /,/g' >> $OUTFILE
+    if [ -f $STOP_SIGNAL_FILE ]; then
+        rm $STOP_SIGNAL_FILE
+        break
+    else
+        sleep $PERIOD
+    fi
+done