Schedule load balance tasklet less frequently
We schedule the tasklet before this patch always with the value in
sd->interval. However, if the queue is busy then it is sufficient
to schedule the tasklet with sd->interval*busy_factor.
So we modify the calculation of the next time to balance by taking
the interval added to last_balance again. This is only the
right value if the idle/busy situation continues as is.
There are two potential trouble spots:
- If the queue was idle and now gets busy then we call rebalance
early. However, that is not a problem because we will then use
the longer interval for the next period.
- If the queue was busy and becomes idle then we potentially
wait too long before rebalancing. However, when the task
goes idle then idle_balance is called. We add another calculation
of the next balance time based on sd->interval in idle_balance
so that we will rebalance soon.
Signed-off-by: Christoph Lameter <[email protected]>
Index: linux-2.6.19-rc4-mm2/kernel/sched.c
===================================================================
--- linux-2.6.19-rc4-mm2.orig/kernel/sched.c 2006-11-03 12:58:39.263918629 -0600
+++ linux-2.6.19-rc4-mm2/kernel/sched.c 2006-11-03 12:59:12.906134941 -0600
@@ -2758,14 +2758,26 @@ out_balanced:
static void idle_balance(int this_cpu, struct rq *this_rq)
{
struct sched_domain *sd;
+ int pulled_task = 0;
+ unsigned long next_balance = jiffies + 60 * HZ;
for_each_domain(this_cpu, sd) {
if (sd->flags & SD_BALANCE_NEWIDLE) {
/* If we've pulled tasks over stop searching: */
- if (load_balance_newidle(this_cpu, this_rq, sd))
+ pulled_task = load_balance_newidle(this_cpu,
+ this_rq, sd);
+ next_balance = min(next_balance,
+ sd->last_balance + sd->balance_interval);
+ if (pulled_task)
break;
}
}
+ if (!pulled_task)
+ /*
+ * We are going idle. next_balance may be set based on
+ * a busy processor. So reset next_balance.
+ */
+ this_rq->next_balance = next_balance;
}
/*
@@ -2890,8 +2902,16 @@ static void rebalance_domains(unsigned l
}
sd->last_balance += interval;
}
+ /*
+ * Calculate the next balancing point assuming that
+ * the idle state does not change. If we are idle and then
+ * start running a process then this will be recalculated.
+ * If we are running a process and then become idle
+ * then idle_balance will reset next_balance so that we
+ * rebalance earlier.
+ */
next_balance = min(next_balance,
- sd->last_balance + sd->balance_interval);
+ sd->last_balance + interval);
}
this_rq->next_balance = next_balance;
}
-
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