[patch 1/5] sched: isolation: introduce vmstat_sync isolcpu flags

[Marcelo Tosatti]

Add a new isolcpus flag "vmstat_sync" to control whether
to sync per-CPU counters to global counters when returning
to userspace.

Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>

Index: linux-2.6-vmstat-update/include/linux/sched/isolation.h
===================================================================
--- linux-2.6-vmstat-update.orig/include/linux/sched/isolation.h
+++ linux-2.6-vmstat-update/include/linux/sched/isolation.h
@@ -15,6 +15,7 @@ enum hk_flags {
 	HK_FLAG_WQ		= (1 << 6),
 	HK_FLAG_MANAGED_IRQ	= (1 << 7),
 	HK_FLAG_KTHREAD		= (1 << 8),
+	HK_FLAG_VMSTAT_SYNC	= (1 << 9),
 };
 
 #ifdef CONFIG_CPU_ISOLATION
Index: linux-2.6-vmstat-update/kernel/sched/isolation.c
===================================================================
--- linux-2.6-vmstat-update.orig/kernel/sched/isolation.c
+++ linux-2.6-vmstat-update/kernel/sched/isolation.c
@@ -173,6 +173,12 @@ static int __init housekeeping_isolcpus_
 			continue;
 		}
 
+		if (!strncmp(str, "vmstat_sync,", 12)) {
+			str += 12;
+			flags |= HK_FLAG_VMSTAT_SYNC;
+			continue;
+		}
+
 		/*
 		 * Skip unknown sub-parameter and validate that it is not
 		 * containing an invalid character.
Index: linux-2.6-vmstat-update/Documentation/admin-guide/kernel-parameters.txt
===================================================================
--- linux-2.6-vmstat-update.orig/Documentation/admin-guide/kernel-parameters.txt
+++ linux-2.6-vmstat-update/Documentation/admin-guide/kernel-parameters.txt
@@ -2124,6 +2124,23 @@
 
 			The format of <cpu-list> is described above.
 
+                        vmstat_sync
+
+			  Page counters are maintained in per-CPU counters to
+			  improve performance. When a CPU modifies a page counter,
+			  this modification is kept in the per-CPU counter.
+			  Certain activities require a global count, which
+			  involves requesting each CPU to flush its local counters
+			  to the global VM counters.
+			  This flush is implemented via a workqueue item, which
+			  requires scheduling the workqueue task on isolated CPUs.
+
+			  To avoid this interruption, this option syncs the
+			  page counters on each return from system calls.
+			  To ensure the application returns to userspace
+  			  with no modified per-CPU counters, its necessary to
+			  use mlockall() in addition to this isolcpus flag.
+
 	iucv=		[HW,NET]
 
 	ivrs_ioapic	[HW,X86-64]