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Subject[PATCH] genirq: change force_irqthreads from bool test to static key
Date
From: Tanner Love <tannerlove@google.com>

With CONFIG_IRQ_FORCED_THREADING=y, testing the bool force_irqthreads
could incur a cache line miss in invoke_softirq().

Replace the test with a static key to avoid the potential cache miss.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Tanner Love <tannerlove@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
drivers/ide/ide-iops.c | 7 +++----
include/linux/interrupt.h | 4 +++-
kernel/irq/manage.c | 6 +++---
3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c
index f2be127ee96e..f86cdb8451e6 100644
--- a/drivers/ide/ide-iops.c
+++ b/drivers/ide/ide-iops.c
@@ -109,7 +109,6 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad,
ide_hwif_t *hwif = drive->hwif;
const struct ide_tp_ops *tp_ops = hwif->tp_ops;
unsigned long flags;
- bool irqs_threaded = force_irqthreads;
int i;
u8 stat;

@@ -117,7 +116,7 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad,
stat = tp_ops->read_status(hwif);

if (stat & ATA_BUSY) {
- if (!irqs_threaded) {
+ if (!force_irqthreads) {
local_save_flags(flags);
local_irq_enable_in_hardirq();
}
@@ -133,13 +132,13 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad,
if ((stat & ATA_BUSY) == 0)
break;

- if (!irqs_threaded)
+ if (!force_irqthreads)
local_irq_restore(flags);
*rstat = stat;
return -EBUSY;
}
}
- if (!irqs_threaded)
+ if (!force_irqthreads)
local_irq_restore(flags);
}
/*
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 4777850a6dc7..9e676c351f23 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>
@@ -504,7 +505,8 @@ extern int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which,
# ifdef CONFIG_PREEMPT_RT
# 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)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 4c14356543d9..395945e54929 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -25,12 +25,12 @@
#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);
+EXPORT_SYMBOL_GPL(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);
--
2.32.0.rc0.204.g9fa02ecfa5-goog
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