Xen devel - Sep 2013 - [PATCH 4/5] xen/spinlock: Don't setup xen spinlock IPI kicker if disabled.

There is no need to setup this IPI kicker if we are never going
to use the paravirtualized ticketlock mechanism.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/xen/spinlock.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 71db82c..e1bff87 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -105,6 +105,7 @@ static DEFINE_PER_CPU(char *, irq_name);
 static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
 static cpumask_t waiting_cpus;
 
+static bool xen_pvspin __initdata = true;
 static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 {
 	int irq = __this_cpu_read(lock_kicker_irq);
@@ -223,6 +224,9 @@ void xen_init_lock_cpu(int cpu)
 	int irq;
 	char *name;
 
+	if (!xen_pvspin)
+		return;
+
 	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on
IRQ%d!\n",
 	     cpu, per_cpu(lock_kicker_irq, cpu));
 
@@ -259,13 +263,15 @@ void xen_uninit_lock_cpu(int cpu)
 	if (xen_hvm_domain())
 		return;
 
+	if (!xen_pvspin)
+		return;
+
 	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 	per_cpu(lock_kicker_irq, cpu) = -1;
 	kfree(per_cpu(irq_name, cpu));
 	per_cpu(irq_name, cpu) = NULL;
 }
 
-static bool xen_pvspin __initdata = true;
 
 void __init xen_init_spinlocks(void)
 {
@@ -305,6 +311,9 @@ static int __init xen_spinlock_debugfs(void)
 	if (d_xen == NULL)
 		return -ENOMEM;
 
+	if (!xen_pvspin)
+		return 0;
+
 	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
 
 	debugfs_create_u8("zero_stats", 0644, d_spin_debug,
&zero_stats);
-- 
1.7.7.6

On 07/09/13 14:46, Konrad Rzeszutek Wilk wrote:
> There is no need to setup this IPI kicker if we are never going
> to use the paravirtualized ticketlock mechanism.
"kicker IPI"

Otherwise,

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

David

Konrad Rzeszutek Wilk wrote:
> There is no need to setup this IPI kicker if we are never going
> to use the paravirtualized ticketlock mechanism.
Excellent patch; the important takeaway is that paravirtualization is
still quite useful in the real world.

There is no need to setup this kicker IPI if we are never going
to use the paravirtualized ticketlock mechanism.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/xen/spinlock.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 71db82c..e1bff87 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -105,6 +105,7 @@ static DEFINE_PER_CPU(char *, irq_name);
 static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
 static cpumask_t waiting_cpus;
 
+static bool xen_pvspin __initdata = true;
 static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 {
 	int irq = __this_cpu_read(lock_kicker_irq);
@@ -223,6 +224,9 @@ void xen_init_lock_cpu(int cpu)
 	int irq;
 	char *name;
 
+	if (!xen_pvspin)
+		return;
+
 	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on
IRQ%d!\n",
 	     cpu, per_cpu(lock_kicker_irq, cpu));
 
@@ -259,13 +263,15 @@ void xen_uninit_lock_cpu(int cpu)
 	if (xen_hvm_domain())
 		return;
 
+	if (!xen_pvspin)
+		return;
+
 	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
 	per_cpu(lock_kicker_irq, cpu) = -1;
 	kfree(per_cpu(irq_name, cpu));
 	per_cpu(irq_name, cpu) = NULL;
 }
 
-static bool xen_pvspin __initdata = true;
 
 void __init xen_init_spinlocks(void)
 {
@@ -305,6 +311,9 @@ static int __init xen_spinlock_debugfs(void)
 	if (d_xen == NULL)
 		return -ENOMEM;
 
+	if (!xen_pvspin)
+		return 0;
+
 	d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
 
 	debugfs_create_u8("zero_stats", 0644, d_spin_debug,
&zero_stats);
-- 
1.8.3.1