Subject: [PATCH] powerpc/powernv: do not process OPAL events from hard interrupt context

From: Nicholas Piggin <[email-masked]>
Date: Fri, 6 Apr 2018 00:46:08 +1000

Using irq_work for processing batches of OPAL events can cause latency
spikes. irq_work is typically used just to schedule work from NMI
context or for work that specifically needs to execute in interrupt
context. If we are to remain with this approach to OPAL events,
softirqs would be a better fit.

But they are not required either. OPAL events are not particularly
performance or latency critical, and we already have kopald to poll
and run events, so have kopald run them all. Rather than scheduling
them as irq_work, just run them directly from kopald. Enable and
disable interrupts between processing each event.

Event handlers themselves should still use threaded handlers,
workqueues, etc. as necessary to avoid high interrupts-off latencies
within any single interrupt.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/platforms/powernv/opal-irqchip.c | 85 ++++++++++++---------------
 arch/powerpc/platforms/powernv/opal.c         | 23 ++++----
 arch/powerpc/platforms/powernv/powernv.h      |  3 +-
 3 files changed, 51 insertions(+), 60 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/opal-irqchip.c b/arch/powerpc/platforms/powernv/opal-irqchip.c
index 9d1b8c0aaf93..646bfac8e3f5 100644
--- a/arch/powerpc/platforms/powernv/opal-irqchip.c
+++ b/arch/powerpc/platforms/powernv/opal-irqchip.c
@@ -22,7 +22,6 @@
 #include <linux/kthread.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
-#include <linux/irq_work.h>
 
 #include <asm/machdep.h>
 #include <asm/opal.h>
@@ -38,37 +37,47 @@ struct opal_event_irqchip {
 	unsigned long mask;
 };
 static struct opal_event_irqchip opal_event_irqchip;
-
+static u64 last_outstanding_events;
 static unsigned int opal_irq_count;
 static unsigned int *opal_irqs;
 
-static void opal_handle_irq_work(struct irq_work *work);
-static u64 last_outstanding_events;
-static struct irq_work opal_event_irq_work = {
-	.func = opal_handle_irq_work,
-};
-
-void opal_handle_events(uint64_t events)
+void opal_handle_events(void)
 {
-	int virq, hwirq = 0;
-	u64 mask = opal_event_irqchip.mask;
+	__be64 events = 0;
+	u64 e;
+
+	e = last_outstanding_events & opal_event_irqchip.mask;
+again:
+	while (e) {
+		int virq, hwirq;
+
+		hwirq = fls64(e) - 1;
+		e &= ~BIT_ULL(hwirq);
+
+		local_irq_disable();
+		virq = irq_find_mapping(opal_event_irqchip.domain, hwirq);
+		if (virq) {
+			irq_enter();
+			generic_handle_irq(virq);
+			irq_exit();
+		}
+		local_irq_enable();
 
-	if (!in_irq() && (events & mask)) {
-		last_outstanding_events = events;
-		irq_work_queue(&opal_event_irq_work);
-		return;
+		cond_resched();
 	}
+	last_outstanding_events = 0;
+	if (opal_poll_events(&events) != OPAL_SUCCESS)
+		return;
+	e = be64_to_cpu(events) & opal_event_irqchip.mask;
+	if (e)
+		goto again;
+}
 
-	while (events & mask) {
-		hwirq = fls64(events) - 1;
-		if (BIT_ULL(hwirq) & mask) {
-			virq = irq_find_mapping(opal_event_irqchip.domain,
-						hwirq);
-			if (virq)
-				generic_handle_irq(virq);
-		}
-		events &= ~BIT_ULL(hwirq);
-	}
+bool opal_recheck_events(void)
+{
+	if (last_outstanding_events & opal_event_irqchip.mask)
+		return true;
+	return false;
 }
 
 static void opal_event_mask(struct irq_data *d)
@@ -78,24 +87,9 @@ static void opal_event_mask(struct irq_data *d)
 
 static void opal_event_unmask(struct irq_data *d)
 {
-	__be64 events;
-
 	set_bit(d->hwirq, &opal_event_irqchip.mask);
-
-	opal_poll_events(&events);
-	last_outstanding_events = be64_to_cpu(events);
-
-	/*
-	 * We can't just handle the events now with opal_handle_events().
-	 * If we did we would deadlock when opal_event_unmask() is called from
-	 * handle_level_irq() with the irq descriptor lock held, because
-	 * calling opal_handle_events() would call generic_handle_irq() and
-	 * then handle_level_irq() which would try to take the descriptor lock
-	 * again. Instead queue the events for later.
-	 */
 	if (last_outstanding_events & opal_event_irqchip.mask)
-		/* Need to retrigger the interrupt */
-		irq_work_queue(&opal_event_irq_work);
+		opal_wake_poller();
 }
 
 static int opal_event_set_type(struct irq_data *d, unsigned int flow_type)
@@ -136,16 +130,13 @@ static irqreturn_t opal_interrupt(int irq, void *data)
 	__be64 events;
 
 	opal_handle_interrupt(virq_to_hw(irq), &events);
-	opal_handle_events(be64_to_cpu(events));
+	last_outstanding_events = be64_to_cpu(events);
+	if (last_outstanding_events & opal_event_irqchip.mask)
+		opal_wake_poller();
 
 	return IRQ_HANDLED;
 }
 
-static void opal_handle_irq_work(struct irq_work *work)
-{
-	opal_handle_events(last_outstanding_events);
-}
-
 static int opal_event_match(struct irq_domain *h, struct device_node *node,
 			    enum irq_domain_bus_token bus_token)
 {
diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index fb13bcabe609..f7c7546e4145 100644
--- a/arch/powerpc/platforms/powernv/opal.c
+++ b/arch/powerpc/platforms/powernv/opal.c
@@ -537,21 +537,15 @@ int opal_hmi_exception_early(struct pt_regs *regs)
 /* HMI exception handler called in virtual mode during check_irq_replay. */
 int opal_handle_hmi_exception(struct pt_regs *regs)
 {
-	s64 rc;
-	__be64 evt = 0;
-
 	/*
 	 * Check if HMI event is available.
-	 * if Yes, then call opal_poll_events to pull opal messages and
-	 * process them.
+	 * if Yes, then call opal_handle_events to process them.
 	 */
 	if (!local_paca->hmi_event_available)
 		return 0;
 
 	local_paca->hmi_event_available = 0;
-	rc = opal_poll_events(&evt);
-	if (rc == OPAL_SUCCESS && evt)
-		opal_handle_events(be64_to_cpu(evt));
+	opal_wake_poller();
 
 	return 1;
 }
@@ -754,14 +748,19 @@ static void __init opal_imc_init_dev(void)
 static int kopald(void *unused)
 {
 	unsigned long timeout = msecs_to_jiffies(opal_heartbeat) + 1;
-	__be64 events;
 
 	set_freezable();
 	do {
 		try_to_freeze();
-		opal_poll_events(&events);
-		opal_handle_events(be64_to_cpu(events));
-		schedule_timeout_interruptible(timeout);
+
+		opal_handle_events();
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (opal_recheck_events())
+			__set_current_state(TASK_RUNNING);
+		else
+			schedule_timeout(timeout);
+
 	} while (!kthread_should_stop());
 
 	return 0;
diff --git a/arch/powerpc/platforms/powernv/powernv.h b/arch/powerpc/platforms/powernv/powernv.h
index 94f17ab1374b..31cf221092df 100644
--- a/arch/powerpc/platforms/powernv/powernv.h
+++ b/arch/powerpc/platforms/powernv/powernv.h
@@ -24,7 +24,8 @@ extern u32 pnv_get_supported_cpuidle_states(void);
 
 extern void pnv_lpc_init(void);
 
-extern void opal_handle_events(uint64_t events);
+extern void opal_handle_events(void);
+extern bool opal_recheck_events(void);
 extern void opal_event_shutdown(void);
 
 bool cpu_core_split_required(void);
-- 
2.16.3