From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 31 Jan 2012 13:01:27 +0100
Subject: genirq: Allow disabling of softirq processing in irq thread context
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: f97f650ab5e13dd1c866b0b94466e89356c64dde
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

The processing of softirqs in irq thread context is a performance gain
for the non-rt workloads of a system, but it's counterproductive for
interrupts which are explicitely related to the realtime
workload. Allow such interrupts to prevent softirq processing in their
thread context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 include/linux/interrupt.h |  2 ++
 include/linux/irq.h       |  4 +++-
 kernel/irq/manage.c       | 13 ++++++++++++-
 kernel/irq/settings.h     | 12 ++++++++++++
 kernel/softirq.c          |  9 +++++++++
 5 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index b6e8164cd1b1..2d6d4806b666 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -62,6 +62,7 @@
  *                interrupt handler after suspending interrupts. For system
  *                wakeup devices users need to implement wakeup detection in
  *                their interrupt handlers.
+ * IRQF_NO_SOFTIRQ_CALL - Do not process softirqs in the irq thread context (RT)
  */
 #define IRQF_SHARED		0x00000080
 #define IRQF_PROBE_SHARED	0x00000100
@@ -75,6 +76,7 @@
 #define IRQF_NO_THREAD		0x00010000
 #define IRQF_EARLY_RESUME	0x00020000
 #define IRQF_COND_SUSPEND	0x00040000
+#define IRQF_NO_SOFTIRQ_CALL	0x00080000
 
 #define IRQF_TIMER		(__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)
 
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 066f8d5cd5c4..1084a499374b 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -72,6 +72,7 @@ enum irqchip_irq_state;
  * IRQ_IS_POLLED		- Always polled by another interrupt. Exclude
  *				  it from the spurious interrupt detection
  *				  mechanism and from core side polling.
+ * IRQ_NO_SOFTIRQ_CALL		- No softirq processing in the irq thread context (RT)
  * IRQ_DISABLE_UNLAZY		- Disable lazy irq disable
  */
 enum {
@@ -99,13 +100,14 @@ enum {
 	IRQ_PER_CPU_DEVID	= (1 << 17),
 	IRQ_IS_POLLED		= (1 << 18),
 	IRQ_DISABLE_UNLAZY	= (1 << 19),
+	IRQ_NO_SOFTIRQ_CALL	= (1 << 20),
 };
 
 #define IRQF_MODIFY_MASK	\
 	(IRQ_TYPE_SENSE_MASK | IRQ_NOPROBE | IRQ_NOREQUEST | \
 	 IRQ_NOAUTOEN | IRQ_MOVE_PCNTXT | IRQ_LEVEL | IRQ_NO_BALANCING | \
 	 IRQ_PER_CPU | IRQ_NESTED_THREAD | IRQ_NOTHREAD | IRQ_PER_CPU_DEVID | \
-	 IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY)
+	 IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY | IRQ_NO_SOFTIRQ_CALL)
 
 #define IRQ_NO_BALANCING_MASK	(IRQ_PER_CPU | IRQ_NO_BALANCING)
 
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 5c0472687ce2..4f7690eecbb2 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -912,7 +912,15 @@ irq_forced_thread_fn(struct irq_desc *desc, struct irqaction *action)
 	irq_finalize_oneshot(desc, action);
 	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 		local_irq_enable();
-	local_bh_enable();
+	/*
+	 * Interrupts which have real time requirements can be set up
+	 * to avoid softirq processing in the thread handler. This is
+	 * safe as these interrupts do not raise soft interrupts.
+	 */
+	if (irq_settings_no_softirq_call(desc))
+		_local_bh_enable();
+	else
+		local_bh_enable();
 	return ret;
 }
 
@@ -1380,6 +1388,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 			irqd_set(&desc->irq_data, IRQD_NO_BALANCING);
 		}
 
+		if (new->flags & IRQF_NO_SOFTIRQ_CALL)
+			irq_settings_set_no_softirq_call(desc);
+
 		if (irq_settings_can_autoenable(desc))
 			irq_startup(desc, true);
 		else
diff --git a/kernel/irq/settings.h b/kernel/irq/settings.h
index 320579d89091..2df2d4445b1e 100644
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -16,6 +16,7 @@ enum {
 	_IRQ_PER_CPU_DEVID	= IRQ_PER_CPU_DEVID,
 	_IRQ_IS_POLLED		= IRQ_IS_POLLED,
 	_IRQ_DISABLE_UNLAZY	= IRQ_DISABLE_UNLAZY,
+	_IRQ_NO_SOFTIRQ_CALL	= IRQ_NO_SOFTIRQ_CALL,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
 };
 
@@ -30,6 +31,7 @@ enum {
 #define IRQ_PER_CPU_DEVID	GOT_YOU_MORON
 #define IRQ_IS_POLLED		GOT_YOU_MORON
 #define IRQ_DISABLE_UNLAZY	GOT_YOU_MORON
+#define IRQ_NO_SOFTIRQ_CALL	GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK	GOT_YOU_MORON
 
@@ -40,6 +42,16 @@ irq_settings_clr_and_set(struct irq_desc *desc, u32 clr, u32 set)
 	desc->status_use_accessors |= (set & _IRQF_MODIFY_MASK);
 }
 
+static inline bool irq_settings_no_softirq_call(struct irq_desc *desc)
+{
+	return desc->status_use_accessors & _IRQ_NO_SOFTIRQ_CALL;
+}
+
+static inline void irq_settings_set_no_softirq_call(struct irq_desc *desc)
+{
+	desc->status_use_accessors |= _IRQ_NO_SOFTIRQ_CALL;
+}
+
 static inline bool irq_settings_is_per_cpu(struct irq_desc *desc)
 {
 	return desc->status_use_accessors & _IRQ_PER_CPU;
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 6c431f0ca1c9..fb0625824682 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -594,6 +594,15 @@ void __local_bh_enable(void)
 }
 EXPORT_SYMBOL(__local_bh_enable);
 
+void _local_bh_enable(void)
+{
+	if (WARN_ON(current->softirq_nestcnt == 0))
+		return;
+	if (--current->softirq_nestcnt == 0)
+		migrate_enable();
+}
+EXPORT_SYMBOL(_local_bh_enable);
+
 int in_serving_softirq(void)
 {
 	return current->flags & PF_IN_SOFTIRQ;
-- 
2.26.2