buildstats: add system state sampling

/proc/[diskstats|meminfo|stat] get sampled and written to the same
proc_<filename>.log files as during normal bootchat logging. This will
allow rendering the CPU, disk and memory usage charts.

Right now sampling happens once a second, triggered by the heartbeat
event.That produces quite a bit of data for long builds, which will be
addressed in a separate commit by storing the data in a more compact
form.

(From OE-Core rev: 6f4e8180b5b4857eaf6caf410fd3a4a41ed85930)

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/buildstats.bbclass

@@ -188,3 +188,27 @@ python run_buildstats () {
 addhandler run_buildstats
 run_buildstats[eventmask] = "bb.event.BuildStarted bb.event.BuildCompleted bb.build.TaskStarted bb.build.TaskSucceeded bb.build.TaskFailed"
 
+python runqueue_stats () {
+    import buildstats
+    from bb import event, runqueue
+    # We should not record any samples before the first task has started,
+    # because that's the first activity shown in the process chart.
+    # Besides, at that point we are sure that the build variables
+    # are available that we need to find the output directory.
+    # The persistent SystemStats is stored in the datastore and
+    # closed when the build is done.
+    system_stats = d.getVar('_buildstats_system_stats', True)
+    if not system_stats and isinstance(e, (bb.runqueue.sceneQueueTaskStarted, bb.runqueue.runQueueTaskStarted)):
+        system_stats = buildstats.SystemStats(d)
+        d.setVar('_buildstats_system_stats', system_stats)
+    if system_stats:
+        # Ensure that we sample at important events.
+        done = isinstance(e, bb.event.BuildCompleted)
+        system_stats.sample(force=done)
+        if done:
+            system_stats.close()
+            d.delVar('_buildstats_system_stats')
+}
+
+addhandler runqueue_stats
+runqueue_stats[eventmask] = "bb.runqueue.sceneQueueTaskStarted bb.runqueue.runQueueTaskStarted bb.event.HeartbeatEvent bb.event.BuildCompleted"

meta/lib/buildstats.py

@@ -0,0 +1,47 @@
+# Implements system state sampling. Called by buildstats.bbclass.
+# Because it is a real Python module, it can hold persistent state,
+# like open log files and the time of the last sampling.
+
+import time
+
+class SystemStats:
+    def __init__(self, d):
+        bn = d.getVar('BUILDNAME', True)
+        bsdir = os.path.join(d.getVar('BUILDSTATS_BASE', True), bn)
+        bb.utils.mkdirhier(bsdir)
+
+        self.proc_files = []
+        for filename in ('diskstats', 'meminfo', 'stat'):
+            # In practice, this class gets instantiated only once in
+            # the bitbake cooker process.  Therefore 'append' mode is
+            # not strictly necessary, but using it makes the class
+            # more robust should two processes ever write
+            # concurrently.
+            self.proc_files.append((filename,
+                                    open(os.path.join(bsdir, 'proc_%s.log' % filename), 'ab')))
+        # Last time that we sampled data.
+        self.last = 0
+        # Minimum number of seconds between recording a sample. This
+        # becames relevant when we get called very often while many
+        # short tasks get started. Sampling during quiet periods
+        # depends on the heartbeat event, which fires less often.
+        self.min_seconds = 1
+
+    def close(self):
+        self.monitor_disk.close()
+        for _, output, _ in self.proc_files:
+            output.close()
+
+    def sample(self, force):
+        now = time.time()
+        if (now - self.last > self.min_seconds) or force:
+            for filename, output in self.proc_files:
+                with open(os.path.join('/proc', filename), 'rb') as input:
+                    data = input.read()
+                    # Unbuffered raw write, less overhead and useful
+                    # in case that we end up with concurrent writes.
+                    os.write(output.fileno(),
+                             ('%.0f\n' % now).encode('ascii') +
+                             data +
+                             b'\n')
+            self.last = now