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SubjectRe: [PATCH 06/12 UPDATED] irq: implement irq_schedule_poll()
Implement and use irq_schedule_poll() to schedule desc->poll_timer
instead of calling mod_timer directly. irq_schedule_poll() is called
with desc->lock held and schedules the timer iff necessary - ie. if
the timer is offline or scheduled to expire later than requested.
This will be used to share desc->poll_timer.

* Jiri and Jonathan pointed out that IRQ_POLL_SLACK of HZ / 1000 would
yield 0 slack on the popular 250HZ config. Adjusted to HZ / 250.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
---
Minor update. IRQ_POLL_SLACK bumped up to HZ / 250.
Thanks.

kernel/irq/spurious.c | 47 +++++++++++++++++++++++++++++++++++++++++------
1 file changed, 41 insertions(+), 6 deletions(-)
Index: work/kernel/irq/spurious.c
===================================================================
--- work.orig/kernel/irq/spurious.c
+++ work/kernel/irq/spurious.c
@@ -23,6 +23,8 @@ enum {

/* IRQ polling common parameters */
IRQ_POLL_INTV = HZ / 100, /* from the good ol' 100HZ tick */
+
+ IRQ_POLL_SLACK = HZ / 250, /* 1 tick slack w/ the popular 250HZ config */
};

int noirqdebug __read_mostly;
@@ -43,6 +45,38 @@ static void print_irq_handlers(struct ir
}
}

+static unsigned long irq_poll_slack(unsigned long intv)
+{
+ return IRQ_POLL_SLACK;
+}
+
+/**
+ * irq_schedule_poll - schedule IRQ poll
+ * @desc: IRQ desc to schedule poll for
+ * @intv: poll interval
+ *
+ * Schedules @desc->poll_timer. If the timer is already scheduled,
+ * it's modified iff jiffies + @intv + slack is before the timer's
+ * expires. poll_timers aren't taken offline behind this function's
+ * back and the users of this function are guaranteed that poll_irq()
+ * will be called at or before jiffies + @intv + slack.
+ *
+ * CONTEXT:
+ * desc->lock
+ */
+static void irq_schedule_poll(struct irq_desc *desc, unsigned long intv)
+{
+ unsigned long expires = jiffies + intv;
+ int slack = irq_poll_slack(intv);
+
+ if (timer_pending(&desc->poll_timer) &&
+ time_before_eq(desc->poll_timer.expires, expires + slack))
+ return;
+
+ set_timer_slack(&desc->poll_timer, slack);
+ mod_timer(&desc->poll_timer, expires);
+}
+
/*
* Recovery handler for misrouted interrupts.
*/
@@ -207,7 +241,9 @@ void __note_interrupt(unsigned int irq,
desc->depth++;
desc->chip->disable(irq);

- mod_timer(&desc->poll_timer, jiffies + IRQ_POLL_INTV);
+ raw_spin_lock(&desc->lock);
+ irq_schedule_poll(desc, IRQ_POLL_INTV);
+ raw_spin_unlock(&desc->lock);
}
desc->irqs_unhandled = 0;
}
@@ -221,9 +257,8 @@ void poll_irq(unsigned long arg)

raw_spin_lock_irq(&desc->lock);
try_one_irq(desc->irq, desc);
+ irq_schedule_poll(desc, IRQ_POLL_INTV);
raw_spin_unlock_irq(&desc->lock);
-
- mod_timer(&desc->poll_timer, jiffies + IRQ_POLL_INTV);
}

void irq_poll_action_added(struct irq_desc *desc, struct irqaction *action)
@@ -238,10 +273,10 @@ void irq_poll_action_added(struct irq_de
__enable_irq(desc, desc->irq, false);
}

- raw_spin_unlock_irqrestore(&desc->lock, flags);
-
if ((action->flags & IRQF_SHARED) && irqfixup >= IRQFIXUP_POLL)
- mod_timer(&desc->poll_timer, jiffies + IRQ_POLL_INTV);
+ irq_schedule_poll(desc, IRQ_POLL_INTV);
+
+ raw_spin_unlock_irqrestore(&desc->lock, flags);
}

void irq_poll_action_removed(struct irq_desc *desc, struct irqaction *action)

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