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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
This commit is contained in:
Tanner Love 2021-06-02 14:03:38 -04:00 committed by Thomas Gleixner
parent 5a6c76b5de
commit 91cc470e79
4 changed files with 12 additions and 11 deletions
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2
block/blk-mq.c
View File

@ -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 */

8
include/linux/interrupt.h
View File

@ -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

11
kernel/irq/manage.c
View File

@ -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;

2
kernel/softirq.c
View File

@ -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