kernel - Improve regressions in usched_dfly (2)

* Allow various fork() behaviors to be supported via
  kern.usched_dfly.features.

* Set the default to place the newly forked process on
  a random cpu instead of the current cpu.

  The bsd4 scheduler had a global queue and could just signal
  a random helper to pick up the thread.  The dfly scheduler
  has per-cpu queues and must actually enqueue the thread to
  another cpu.

  The bsd4 scheduler is still slightly superior here because
  if the parent running on the current cpu immediately waits
  for the child, the child is able to run on the current cpu.
  However, randomization works quite well and this removes
  nearly all of the make -j N regression.

diff --git a/sys/kern/usched_dfly.c b/sys/kern/usched_dfly.c
index 214012b..f276bf5 100644 (file)
--- a/sys/kern/usched_dfly.c
+++ b/sys/kern/usched_dfly.c
@@ -226,18 +226,32 @@ SYSCTL_INT(_debug, OID_AUTO, dfly_chooser, CTLFLAG_RW,
  *          For heavier loads, '35' is a good setting which will still
  *          be fairly optimal at lighter loads.
  *
- *          For extreme loads, '55' is a good setting because you want to
- *          force the pairs together.
+ *          For extreme loads you can try a higher value like '55', or you
+ *          can actually force dispersal by setting a small negative value
+ *          like -15.
  *
  *          15: Fewer threads.
  *          35: Heavily loaded.        (default)
- *          50: Very heavily loaded.
+ *          50: Very heavily loaded.   (not recommended)
+ *          -15: Extreme loads
  *
  * weight3 - Weighting based on the number of runnable threads on the
  *          userland scheduling queue and ignoring their loads.
  *          A nominal value here prevents high-priority (low-load)
  *          threads from accumulating on one cpu core when other
  *          cores are available.
+ *
+ * features - These flags can be set or cleared to enable or disable various
+ *           features.
+ *
+ *           0x01      Pull when cpu becomes idle              (default)
+ *           0x02
+ *           0x04      Enable rebalancing rover                (default)
+ *           0x08
+ *           0x10
+ *           0x20      choose best cpu for forked process
+ *           0x40      choose current cpu for forked process
+ *           0x80      choose random cpu for forked process    (default)
  */
 #ifdef SMP
 static int usched_dfly_smt = 0;
@@ -245,7 +259,7 @@ static int usched_dfly_cache_coherent = 0;
 static int usched_dfly_weight1 = 50;   /* keep thread on current cpu */
 static int usched_dfly_weight2 = 35;   /* synchronous peer's current cpu */
 static int usched_dfly_weight3 = 10;   /* number of threads on queue */
-static int usched_dfly_features = 15;  /* allow pulls */
+static int usched_dfly_features = 0x8F;        /* allow pulls */
 #endif
 static int usched_dfly_rrinterval = (ESTCPUFREQ + 9) / 10;
 static int usched_dfly_decay = 8;
@@ -685,11 +699,16 @@ dfly_setrunqueue(struct lwp *lp)
         */
        if (lp->lwp_forked) {
                lp->lwp_forked = 0;
-               if (dfly_pcpu[lp->lwp_qcpu].runqcount)
+               if (usched_dfly_features & 0x20)
+                       rdd = dfly_choose_best_queue(lp);
+               else if (usched_dfly_features & 0x40)
+                       rdd = &dfly_pcpu[lp->lwp_qcpu];
+               else if (usched_dfly_features & 0x80)
+                       rdd = dfly_choose_queue_simple(rdd, lp);
+               else if (dfly_pcpu[lp->lwp_qcpu].runqcount)
                        rdd = dfly_choose_best_queue(lp);
                else
                        rdd = &dfly_pcpu[lp->lwp_qcpu];
-               /* dfly_wakeup_random_helper(rdd); */
        } else {
                rdd = dfly_choose_best_queue(lp);
                /* rdd = &dfly_pcpu[lp->lwp_qcpu]; */