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Old 06-25-2012, 09:55 AM
Stefan Bader
Default UBUNTU: SAUCE: Use ticket locks for Xen 3.0.2+

The SUSE patchset did limit the ticket lock code to be used only
on Xen hypervisors version 3.2 or higher because HYPERVISOR_poll()
is supposed to have issues before.
However we have been using that call before and the chance to be
running on EC2 on such an old hypervisor is getting even less.
Not using ticket locks and the hypervisor assisting could increase
host cpu usage and unfairness in lock contention situations.

BugLink: http://bugs.launchpad.net/bugs/929941

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
arch/x86/include/mach-xen/asm/spinlock_types.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/mach-xen/asm/spinlock_types.h b/arch/x86/include/mach-xen/asm/spinlock_types.h
index 7d01ae1..3fa1833 100644
--- a/arch/x86/include/mach-xen/asm/spinlock_types.h
+++ b/arch/x86/include/mach-xen/asm/spinlock_types.h
@@ -13,7 +13,7 @@ typedef union {
* Xen versions prior to 3.2.x have a race condition with HYPERVISOR_poll().
-#if CONFIG_XEN_COMPAT >= 0x030200
+#if CONFIG_XEN_COMPAT >= 0x030002
* On Xen we support a single level of interrupt re-enabling per lock. Hence
* we can have twice as many outstanding tickets. Thus the cut-off for using

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