xen, pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Link: http://lkml.kernel.org/r/1376058122-8248-7-git-send-email-raghavendra.kt@linux.vnet.ibm.com
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/xen/spinlock.c

@@ -244,6 +244,8 @@ void xen_uninit_lock_cpu(int cpu)
 	per_cpu(irq_name, cpu) = NULL;
 }
 
+static bool xen_pvspin __initdata = true;
+
 void __init xen_init_spinlocks(void)
 {
 	/*
@@ -253,10 +255,22 @@ void __init xen_init_spinlocks(void)
 	if (xen_hvm_domain())
 		return;
 
+	if (!xen_pvspin) {
+		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+		return;
+	}
+
 	pv_lock_ops.lock_spinning = xen_lock_spinning;
 	pv_lock_ops.unlock_kick = xen_unlock_kick;
 }
 
+static __init int xen_parse_nopvspin(char *arg)
+{
+	xen_pvspin = false;
+	return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+
 #ifdef CONFIG_XEN_DEBUG_FS
 
 static struct dentry *d_spin_debug;