The following commit has been merged into the irq/core branch of tip:
Commit-ID: af5b7fe6bb77ac775d446e2f25f013d5df551e9a
Gitweb: https://git.kernel.org/tip/af5b7fe6bb77ac775d446e2f25f013d5df551e9a
Author: Tanner Love <tannerlove@xxxxxxxxxx>
AuthorDate: Wed, 02 Jun 2021 14:03:38 -04:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Aug 2021 16:06:55 +02:00
genirq: Change force_irqthreads to a static key
With CONFIG_IRQ_FORCED_THREADING=y, testing the boolean force_irqthreads
could incur a cache line miss in invoke_softirq() and other places.
Replace the test with a static key to avoid the potential cache miss.
[ tglx: Dropped the IDE part, removed the export and updated blk-mq ]
Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Tanner Love <tannerlove@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210602180338.3324213-1-tannerlove.kernel@xxxxxxxxx
---
block/blk-mq.c | 2 +-
include/linux/interrupt.h | 8 +++++---
kernel/irq/manage.c | 9 ++++-----
kernel/softirq.c | 2 +-
4 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c4ac51..572d8ab 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -606,7 +606,7 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq)
* This is probably worse than completing the request on a different
* cache domain.
*/
- if (force_irqthreads)
+ if (force_irqthreads())
return false;
/* same CPU or cache domain? Complete locally */
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2ed65b0..1f22a30 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -13,6 +13,7 @@
#include <linux/hrtimer.h>
#include <linux/kref.h>
#include <linux/workqueue.h>
+#include <linux/jump_label.h>
#include <linux/atomic.h>
#include <asm/ptrace.h>
@@ -474,12 +475,13 @@ extern int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
#ifdef CONFIG_IRQ_FORCED_THREADING
# ifdef CONFIG_PREEMPT_RT
-# define force_irqthreads (true)
+# define force_irqthreads() (true)
# else
-extern bool force_irqthreads;
+DECLARE_STATIC_KEY_FALSE(force_irqthreads_key);
+# define force_irqthreads() (static_branch_unlikely(&force_irqthreads_key))
# endif
#else
-#define force_irqthreads (0)
+#define force_irqthreads() (false)
#endif
#ifndef local_softirq_pending
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 766468a..bb3c51d 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -25,12 +25,11 @@
#include "internals.h"
#if defined(CONFIG_IRQ_FORCED_THREADING) && !defined(CONFIG_PREEMPT_RT)
-__read_mostly bool force_irqthreads;
-EXPORT_SYMBOL_GPL(force_irqthreads);
+DEFINE_STATIC_KEY_FALSE(force_irqthreads_key);
static int __init setup_forced_irqthreads(char *arg)
{
- force_irqthreads = true;
+ static_branch_enable(&force_irqthreads_key);
return 0;
}
early_param("threadirqs", setup_forced_irqthreads);
@@ -1260,8 +1259,8 @@ static int irq_thread(void *data)
irqreturn_t (*handler_fn)(struct irq_desc *desc,
struct irqaction *action);
- if (force_irqthreads && test_bit(IRQTF_FORCED_THREAD,
- &action->thread_flags))
+ if (force_irqthreads() && test_bit(IRQTF_FORCED_THREAD,
+ &action->thread_flags))
handler_fn = irq_forced_thread_fn;
else
handler_fn = irq_thread_fn;
diff --git a/kernel/softirq.c b/kernel/softirq.c
index f3a0121..322b65d 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -422,7 +422,7 @@ static inline void invoke_softirq(void)
if (ksoftirqd_running(local_softirq_pending()))
return;
- if (!force_irqthreads || !__this_cpu_read(ksoftirqd)) {
+ if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) {
#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
/*
* We can safely execute softirq on the current stack if
|