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Subject: genirq: Allow disabling of softirq processing in irq thread context
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 31 Jan 2012 13:01:27 +0100
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.10-rt8.tar.xz
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>
---
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(-)
--- 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)
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -69,6 +69,7 @@ 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 {
@@ -96,13 +97,14 @@ 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)
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -970,7 +970,15 @@ irq_forced_thread_fn(struct irq_desc *de
atomic_inc(&desc->threads_handled);
irq_finalize_oneshot(desc, action);
- 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;
}
@@ -1480,6 +1488,9 @@ static int
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, IRQ_RESEND, IRQ_START_COND);
} else {
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -17,6 +17,7 @@ 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,
};
@@ -31,6 +32,7 @@ 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
@@ -41,6 +43,16 @@ irq_settings_clr_and_set(struct irq_desc
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;
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -598,6 +598,15 @@ 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;
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