From: Thomas Gleixner <tglx@linutronix.de>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: "Nicholas Piggin" <npiggin@gmail.com>,
"Cédric Le Goater" <clg@kaod.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] genirq: reduce irqdebug bouncing cachelines
Date: Sat, 10 Apr 2021 13:58:02 +0200 [thread overview]
Message-ID: <87im4u2vxx.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210402132037.574661-1-npiggin@gmail.com>
Nicholas,
On Fri, Apr 02 2021 at 23:20, Nicholas Piggin wrote:
> note_interrupt increments desc->irq_count for each interrupt even for
> percpu interrupt handlers, even when they are handled successfully. This
> causes cacheline bouncing and limits scalability.
>
> Instead of incrementing irq_count every time, only start incrementing it
> after seeing an unhandled irq, which should avoid the cache line
> bouncing in the common path.
>
> This actually should give better consistency in handling misbehaving
> irqs too, because instead of the first unhandled irq arriving at an
> arbitrary point in the irq_count cycle, its arrival will begin the
> irq_count cycle.
I've applied that because it makes sense in general, but I think the whole
call to note_interrupt() can be avoided or return early when interrupts
would be marked accordingly. For IPI handlers which always return
HANDLED the whole procedure is pretty pointless to begin with.
Something like the completely untested below.
Thanks,
tglx
---
include/linux/interrupt.h | 3 +++
include/linux/irq.h | 2 ++
kernel/irq/manage.c | 2 ++
kernel/irq/settings.h | 12 ++++++++++++
kernel/irq/spurious.c | 2 +-
5 files changed, 20 insertions(+), 1 deletion(-)
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -64,6 +64,8 @@
* IRQF_NO_AUTOEN - Don't enable IRQ or NMI automatically when users request it.
* Users will enable it explicitly by enable_irq() or enable_nmi()
* later.
+ * IRQF_NO_DEBUG - Exclude from runnaway detection for IPI and similar handlers,
+ * depends on IRQF_PERCPU.
*/
#define IRQF_SHARED 0x00000080
#define IRQF_PROBE_SHARED 0x00000100
@@ -78,6 +80,7 @@
#define IRQF_EARLY_RESUME 0x00020000
#define IRQF_COND_SUSPEND 0x00040000
#define IRQF_NO_AUTOEN 0x00080000
+#define IRQF_NO_DEBUG 0x00100000
#define IRQF_TIMER (__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -72,6 +72,7 @@ enum irqchip_irq_state;
* mechanism and from core side polling.
* IRQ_DISABLE_UNLAZY - Disable lazy irq disable
* IRQ_HIDDEN - Don't show up in /proc/interrupts
+ * IRQ_NO_DEBUG - Exclude from note_interrupt() debugging
*/
enum {
IRQ_TYPE_NONE = 0x00000000,
@@ -99,6 +100,7 @@ enum {
IRQ_IS_POLLED = (1 << 18),
IRQ_DISABLE_UNLAZY = (1 << 19),
IRQ_HIDDEN = (1 << 20),
+ IRQ_NO_DEBUG = (1 << 21),
};
#define IRQF_MODIFY_MASK \
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1682,6 +1682,8 @@ static int
if (new->flags & IRQF_PERCPU) {
irqd_set(&desc->irq_data, IRQD_PER_CPU);
irq_settings_set_per_cpu(desc);
+ if (new->flags & IRQF_NO_DEBUG)
+ irq_settings_set_no_debug(desc);
}
if (new->flags & IRQF_ONESHOT)
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -18,6 +18,7 @@ enum {
_IRQ_IS_POLLED = IRQ_IS_POLLED,
_IRQ_DISABLE_UNLAZY = IRQ_DISABLE_UNLAZY,
_IRQ_HIDDEN = IRQ_HIDDEN,
+ _IRQ_NO_DEBUG = IRQ_NO_DEBUG,
_IRQF_MODIFY_MASK = IRQF_MODIFY_MASK,
};
@@ -33,6 +34,7 @@ enum {
#define IRQ_IS_POLLED GOT_YOU_MORON
#define IRQ_DISABLE_UNLAZY GOT_YOU_MORON
#define IRQ_HIDDEN GOT_YOU_MORON
+#define IRQ_NO_DEBUG GOT_YOU_MORON
#undef IRQF_MODIFY_MASK
#define IRQF_MODIFY_MASK GOT_YOU_MORON
@@ -174,3 +176,13 @@ static inline bool irq_settings_is_hidde
{
return desc->status_use_accessors & _IRQ_HIDDEN;
}
+
+static inline void irq_settings_set_no_debug(struct irq_desc *desc)
+{
+ desc->status_use_accessors |= _IRQ_NO_DEBUG;
+}
+
+static inline bool irq_settings_no_debug(struct irq_desc *desc)
+{
+ return desc->status_use_accessors & _IRQ_NO_DEBUG;
+}
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -274,7 +274,7 @@ void note_interrupt(struct irq_desc *des
unsigned int irq;
if (desc->istate & IRQS_POLL_INPROGRESS ||
- irq_settings_is_polled(desc))
+ irq_settings_is_polled(desc) | irq_settings_no_debug(desc))
return;
if (bad_action_ret(action_ret)) {
next prev parent reply other threads:[~2021-04-10 11:58 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-02 13:20 [PATCH] genirq: reduce irqdebug bouncing cachelines Nicholas Piggin
2021-04-10 11:38 ` [tip: irq/core] genirq: Reduce irqdebug cacheline bouncing tip-bot2 for Nicholas Piggin
2021-04-10 11:58 ` Thomas Gleixner [this message]
2021-04-12 9:06 ` [PATCH] genirq: reduce irqdebug bouncing cachelines Cédric Le Goater
2021-04-12 12:43 ` Thomas Gleixner
2021-04-13 12:16 ` Cédric Le Goater
2021-04-13 20:24 ` Thomas Gleixner
2021-04-14 13:13 ` Cédric Le Goater
2021-05-15 17:01 ` Cédric Le Goater
2021-05-17 18:04 ` [tip: irq/core] genirq: Add a IRQF_NO_DEBUG flag tip-bot2 for Thomas Gleixner
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