bitbake: runqueue: Fix performance of multiconfigs with large overlap

There have been complaints about the performance of large multiconfig builds
for a while. The key missing data point was that the builds needed to have large
overlaps in sstate objects. This can be simulated by building the same things with
just different TMPDIRs. In runqueue/bitbake terms this equates to large numbers of
deferred tasks.

The issue is that the expensive checks in the setscene loop were hit every time
through runqueue's execute function before the check on deferred tasks. This leads
to task execution starvation as that only happens once per iteration.

Move the skip check earlier in the function which speeds things up enormously
and should improve performance of such builds for users.

(Bitbake rev: 9c6c506757f2b3e28c8b20513b45da6b4659c95f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/runqueue.py

@@ -2210,6 +2210,9 @@ class RunQueueExecute:
             # Find the next setscene to run
             for nexttask in self.sorted_setscene_tids:
                 if nexttask in self.sq_buildable and nexttask not in self.sq_running and self.sqdata.stamps[nexttask] not in self.build_stamps.values() and nexttask not in self.sq_harddep_deferred:
+                    if nexttask in self.sq_deferred and self.sq_deferred[nexttask] not in self.runq_complete:
+                        # Skip deferred tasks quickly before the 'expensive' tests below - this is key to performant multiconfig builds
+                        continue
                     if nexttask not in self.sqdata.unskippable and self.sqdata.sq_revdeps[nexttask] and \
                             nexttask not in self.sq_needed_harddeps and \
                             self.sqdata.sq_revdeps[nexttask].issubset(self.scenequeue_covered) and \
@@ -2239,8 +2242,7 @@ class RunQueueExecute:
                         if t in self.runq_running and t not in self.runq_complete:
                             continue
                     if nexttask in self.sq_deferred:
-                        if self.sq_deferred[nexttask] not in self.runq_complete:
-                            continue
+                        # Deferred tasks that were still deferred were skipped above so we now need to process
                         logger.debug("Task %s no longer deferred" % nexttask)
                         del self.sq_deferred[nexttask]
                         valid = self.rq.validate_hashes(set([nexttask]), self.cooker.data, 0, False, summary=False)