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@google.com>
Signed-off-by: Tanner Love <tannerlove@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210602180338.3324213-1-tannerlove.kernel@gmail.com

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c4ac51..572d8ab 100644 (file)
--- 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 (file)
--- 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..34a66c4 100644 (file)
--- 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;
@@ -1322,7 +1321,7 @@ EXPORT_SYMBOL_GPL(irq_wake_thread);
 
 static int irq_setup_forced_threading(struct irqaction *new)
 {
-       if (!force_irqthreads)
+       if (!force_irqthreads())
                return 0;
        if (new->flags & (IRQF_NO_THREAD | IRQF_PERCPU | IRQF_ONESHOT))
                return 0;

diff --git a/kernel/softirq.c b/kernel/softirq.c
index f3a0121..322b65d 100644 (file)
--- 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