linux-kernel - Re: v2.6.21.4-rt11

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Date:	Mon, 18 Jun 2007 10:59:21 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	suresh.b.siddha@...el.com, pwil3058@...pond.net.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: v2.6.21.4-rt11

On Mon, 18 Jun 2007, Srivatsa Vaddagiri wrote:

> On Mon, Jun 18, 2007 at 09:54:18AM -0700, Christoph Lameter wrote:
> > The nodes-level domain looks for internode balances between up to 16 
> > nodes. It is not restricted to a single node.
> 
> I was mostly speaking with the example system in mind (4-node 4-cpu
> box), but yes, node-level domain does look for imbalance across max 16
> nodes as you mention.
> 
> Both node and all-node domains don't have SD_BALANCE_NEWIDLE set, which
> means idle_balance() will stop looking for imbalance beyonds its own
> node. Based on the observed balance within its own node, IMO,
> idle_balance() should not cause ->next_balance to be reset.

I think the check in idle_balance needs to be modified.

If the domain *does not* have SD_BALANCE_NEWIDLE set then
next_balance must still be set right. Does this patch fix it?



Scheduler: Fix next_interval determination in idle_balance().

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.

Signed-off-by: Christop Lameter <clameter@....com>

Index: linux-2.6.22-rc4-mm2/kernel/sched.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/kernel/sched.c	2007-06-18 10:56:31.000000000 -0700
+++ linux-2.6.22-rc4-mm2/kernel/sched.c	2007-06-18 10:57:10.000000000 -0700
@@ -2493,17 +2493,16 @@ static void idle_balance(int this_cpu, s
 	unsigned long next_balance = jiffies + 60 *  HZ;
 
 	for_each_domain(this_cpu, sd) {
-		if (sd->flags & SD_BALANCE_NEWIDLE) {
+		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;
-		}
+		if (time_after(next_balance,
+			  sd->last_balance + sd->balance_interval))
+			next_balance = sd->last_balance
+					+ sd->balance_interval;
+		if (pulled_task)
+			break;
 	}
 	if (!pulled_task)
 		/*
-
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