linux-kernel - [PATCH] sched: revert load_balance

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Message-Id: <1203942167.6242.142.camel@lappy>
Date:	Mon, 25 Feb 2008 13:22:47 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched: revert load_balance_monitor()

Subject: sched: revert load_balance_monitor()

The following commit causes a number of serious regressions:

  commit 6b2d7700266b9402e12824e11e0099ae6a4a6a79
  Author: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
  Date:   Fri Jan 25 21:08:00 2008 +0100
  sched: group scheduler, fix fairness of cpu bandwidth allocation for task groups

Namely:
 - very frequent wakeups on SMP, reported by PowerTop users.
 - cacheline trashing on (large) SMP
 - some latencies larger than 500ms

While there is a mergeable patch to fix the latter, the former issues
are IMHO not fixable in a manner suitable for .25 (we're at -rc3 now).
Hence I propose to revert this patch and try again for .26.

( minimal revert - leaves most of the code present, just removes the activation
  and sysctl interface ).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
---
 include/linux/sched.h |    4 ----
 kernel/sched.c        |   15 ---------------
 kernel/sysctl.c       |   18 ------------------
 3 files changed, 37 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1541,10 +1541,6 @@ extern unsigned int sysctl_sched_child_r
 extern unsigned int sysctl_sched_features;
 extern unsigned int sysctl_sched_migration_cost;
 extern unsigned int sysctl_sched_nr_migrate;
-#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
-extern unsigned int sysctl_sched_min_bal_int_shares;
-extern unsigned int sysctl_sched_max_bal_int_shares;
-#endif
 
 int sched_nr_latency_handler(struct ctl_table *table, int write,
 		struct file *file, void __user *buffer, size_t *length,
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -7083,21 +7083,6 @@ void __init sched_init_smp(void)
 	if (set_cpus_allowed(current, non_isolated_cpus) < 0)
 		BUG();
 	sched_init_granularity();
-
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	if (nr_cpu_ids == 1)
-		return;
-
-	lb_monitor_task = kthread_create(load_balance_monitor, NULL,
-					 "group_balance");
-	if (!IS_ERR(lb_monitor_task)) {
-		lb_monitor_task->flags |= PF_NOFREEZE;
-		wake_up_process(lb_monitor_task);
-	} else {
-		printk(KERN_ERR "Could not create load balance monitor thread"
-			"(error = %ld) \n", PTR_ERR(lb_monitor_task));
-	}
-#endif
 }
 #else
 void __init sched_init_smp(void)
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -311,24 +311,6 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
-#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
-	{
-		.ctl_name       = CTL_UNNUMBERED,
-		.procname       = "sched_min_bal_int_shares",
-		.data           = &sysctl_sched_min_bal_int_shares,
-		.maxlen         = sizeof(unsigned int),
-		.mode           = 0644,
-		.proc_handler   = &proc_dointvec,
-	},
-	{
-		.ctl_name       = CTL_UNNUMBERED,
-		.procname       = "sched_max_bal_int_shares",
-		.data           = &sysctl_sched_max_bal_int_shares,
-		.maxlen         = sizeof(unsigned int),
-		.mode           = 0644,
-		.proc_handler   = &proc_dointvec,
-	},
-#endif
 #endif
 	{
 		.ctl_name	= CTL_UNNUMBERED,


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