svn commit: r336855 - head/sys/kern

[Don Lewis]

Author: truckman
Date: Sun Jul 29 00:30:06 2018
New Revision: 336855
URL: https://svnweb.freebsd.org/changeset/base/336855

Log:
  Fix the long term ULE load balancer so that it actually works.  The
  initial call to sched_balance() during startup is meant to initialize
  balance_ticks, but does not actually do that since smp_started is
  still zero at that time.  Since balance_ticks does not get set,
  there are no further calls to sched_balance().  Fix this by setting
  balance_ticks in sched_initticks() since we know the value of
  balance_interval at that time, and eliminate the useless startup
  call to sched_balance().  We don't need to randomize the intial
  value of balance_ticks.
  
  Since there is now only one call to sched_balance(), we can hoist
  the tests at the top of this function out to the caller and avoid
  the overhead of the function call when running a SMP kernel on UP
  hardware.
  
  PR:		223914
  Reviewed by:	kib
  MFC after:	2 weeks

Modified:
  head/sys/kern/sched_ule.c

Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c	Sun Jul 29 00:12:16 2018	(r336854)
+++ head/sys/kern/sched_ule.c	Sun Jul 29 00:30:06 2018	(r336855)
@@ -884,9 +884,6 @@ sched_balance(void)
 {
 	struct tdq *tdq;
 
-	if (smp_started == 0 || rebalance == 0)
-		return;
-
 	balance_ticks = max(balance_interval / 2, 1) +
 	    (sched_random() % balance_interval);
 	tdq = TDQ_SELF();
@@ -1413,7 +1410,6 @@ sched_setup_smp(void)
 			panic("Can't find cpu group for %d\n", i);
 	}
 	balance_tdq = TDQ_SELF();
-	sched_balance();
 }
 #endif
 
@@ -1474,6 +1470,7 @@ sched_initticks(void *dummy)
 	 * what realstathz is.
 	 */
 	balance_interval = realstathz;
+	balance_ticks = balance_interval;
 	affinity = SCHED_AFFINITY_DEFAULT;
 #endif
 	if (sched_idlespinthresh < 0)
@@ -2382,7 +2379,7 @@ sched_clock(struct thread *td)
 	/*
 	 * We run the long term load balancer infrequently on the first cpu.
 	 */
-	if (balance_tdq == tdq) {
+	if (balance_tdq == tdq && smp_started != 0 && rebalance != 0) {
 		if (balance_ticks && --balance_ticks == 0)
 			sched_balance();
 	}