MINOR: task: give the scheduler a bit more flexibility in the runqueue size

Instead of setting a hard-limit on runqueue-depth and keeping it short
to maintain fairness, let's allow the scheduler to automatically cut
the existing one in two equal halves if its size is between the configured
size and its double. This will allow to increase the default value while
keeping a low latency.

(cherry picked from commit 1691ba3693d4b11cc85aed606d39ffbd23d8533f)
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/src/task.c b/src/task.c
index 2959812..92d9630 100644 (file)
--- a/src/task.c
+++ b/src/task.c
@@ -591,6 +591,13 @@ void process_runnable_tasks()
        if (likely(niced_tasks))
                max_processed = (max_processed + 3) / 4;
 
+       if (max_processed < sched->rq_total && sched->rq_total <= 2*max_processed) {
+               /* If the run queue exceeds the budget by up to 50%, let's cut it
+                * into two identical halves to improve latency.
+                */
+               max_processed = sched->rq_total / 2;
+       }
+
  not_done_yet:
        max[TL_URGENT] = max[TL_NORMAL] = max[TL_BULK] = 0;