sched: fix next_interval determination in idle_balance()

Fix massive SMP imbalance on NUMA nodes observed on 2.6.21.5 with CFS.
(and later on reproduced without CFS as well).

The intervals of domains that do not have SD_BALANCE_NEWIDLE must be
considered for the calculation of the time of the next balance.
Otherwise we may defer rebalancing forever and nodes might stay idle for
very long times.

Siddha also spotted that the conversion of the balance interval to
jiffies is missing. Fix that to.

From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

also continue the loop if !(sd->flags & SD_LOAD_BALANCE).

Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
It did in fact trigger under all three of mainline, CFS, and -rt
including CFS -- see below for a couple of emails from last Friday
giving results for these three on the AMD box (where it happened) and on
a single-quad NUMA-Q system (where it did not, at least not with such
severity).

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/sched.c b/kernel/sched.c
index a3993b9e7503a9aa033dc398989845388fa3e3de..f745a4437138f88af88de973dd15b170e446593d 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2831,17 +2831,21 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
        unsigned long next_balance = jiffies + 60 *  HZ;
 
        for_each_domain(this_cpu, sd) {
-               if (sd->flags & SD_BALANCE_NEWIDLE) {
+               unsigned long interval;
+
+               if (!(sd->flags & SD_LOAD_BALANCE))
+                       continue;
+
+               if (sd->flags & SD_BALANCE_NEWIDLE)
                        /* If we've pulled tasks over stop searching: */
                        pulled_task = load_balance_newidle(this_cpu,
-                                                       this_rq, sd);
-                       if (time_after(next_balance,
-                                 sd->last_balance + sd->balance_interval))
-                               next_balance = sd->last_balance
-                                               + sd->balance_interval;
-                       if (pulled_task)
-                               break;
-               }
+                                                               this_rq, sd);
+
+               interval = msecs_to_jiffies(sd->balance_interval);
+               if (time_after(next_balance, sd->last_balance + interval))
+                       next_balance = sd->last_balance + interval;
+               if (pulled_task)
+                       break;
        }
        if (!pulled_task)
                /*