genirq: Allow disabling of softirq processing in irq thread context

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>
Cc: stable-rt@vger.kernel.org

3 files changed, 31 insertions, 1 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index b3e622849807..87dc0539cebb 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -742,7 +742,15 @@ irq_forced_thread_fn(struct irq_desc *desc, struct irqaction *action)
 	local_bh_disable();
 	ret = action->thread_fn(action->irq, action->dev_id);
 	irq_finalize_oneshot(desc, action, false);
-	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;
 }
 
@@ -1072,6 +1080,9 @@ __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);
+
 		/* Set default affinity mask once everything is setup */
 		setup_affinity(irq, desc, mask);
 
diff --git a/kernel/irq/settings.h b/kernel/irq/settings.h
index 1162f1030f18..0d2c381c2bdb 100644
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -14,6 +14,7 @@ enum {
 	_IRQ_NO_BALANCING	= IRQ_NO_BALANCING,
 	_IRQ_NESTED_THREAD	= IRQ_NESTED_THREAD,
 	_IRQ_PER_CPU_DEVID	= IRQ_PER_CPU_DEVID,
+	_IRQ_NO_SOFTIRQ_CALL	= IRQ_NO_SOFTIRQ_CALL,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
 };
 
@@ -26,6 +27,7 @@ enum {
 #define IRQ_NOAUTOEN		GOT_YOU_MORON
 #define IRQ_NESTED_THREAD	GOT_YOU_MORON
 #define IRQ_PER_CPU_DEVID	GOT_YOU_MORON
+#define IRQ_NO_SOFTIRQ_CALL	GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK	GOT_YOU_MORON
 
@@ -36,6 +38,16 @@ 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 92b4ca30eda2..bef08f3cd6d6 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -425,6 +425,13 @@ void local_bh_enable_ip(unsigned long ip)
 }
 EXPORT_SYMBOL(local_bh_enable_ip);
 
+void _local_bh_enable(void)
+{
+	current->softirq_nestcnt--;
+	migrate_enable();
+}
+EXPORT_SYMBOL(_local_bh_enable);
+
 /* For tracing */
 int notrace __in_softirq(void)
 {