[PATCH 1/3] ARCv2: intc: Fix random perf irq disabling in SMP setup

[PATCH 1/3] ARCv2: intc: Fix random perf irq disabling in SMP setup

[Vineet Gupta]

As part of fixing another perf issue, observed that after a perf run,
the interrupt got disabled on one/more cores.

| [ARCLinux]# cat /proc/interrupts | grep perf
|  20:    0      0      0       0  ARCv2 core Intc  20 ARC perf counters
|
| [ARCLinux]# perf record -c 20000 /sbin/hackbench
| Running with 10*40 (== 400) tasks.
|
| [ARCLinux]# cat /proc/interrupts | grep perf
|  20:    0    522      8    51916  ARCv2 core Intc  20 ARC perf counters
|
| [ARCLinux]# perf record -c 20000 /sbin/hackbench
| Running with 10*40 (== 400) tasks.
|
| [ARCLinux]# cat /proc/interrupts | grep perf
|  20:    0    522      8   104368  ARCv2 core Intc  20 ARC perf counters

Turns out that despite requesting perf irq as percpu, the flow handler
registered was not handle_percpu_irq()

Given that on ARCv2 cores, IRQs < 24 are always private to cpu, we
register the right handler at the very onset.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: stable@vger.kernel.org #4.2+
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/kernel/intc-arcv2.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
index 26c156827479..0394f9f61b46 100644
--- a/arch/arc/kernel/intc-arcv2.c
+++ b/arch/arc/kernel/intc-arcv2.c
@@ -106,10 +106,21 @@ static struct irq_chip arcv2_irq_chip = {
 static int arcv2_irq_map(struct irq_domain *d, unsigned int irq,
 			 irq_hw_number_t hw)
 {
-	if (irq == TIMER0_IRQ || irq == IPI_IRQ)
+	/*
+	 * core intc IRQs [16, 23]:
+	 * Statically assigned always private-per-core (Timers, WDT, IPI, PCT)
+	 */
+	if (hw < 24) {
+		/*
+		 * A subsequent request_percpu_irq() fails if percpu_devid is
+		 * not set. That in turns sets NOAUTOEN, meaning each core needs
+		 * to call enable_percpu_irq()
+		 */
+		irq_set_percpu_devid(irq);
 		irq_set_chip_and_handler(irq, &arcv2_irq_chip, handle_percpu_irq);
-	else
+	} else {
 		irq_set_chip_and_handler(irq, &arcv2_irq_chip, handle_level_irq);
+	}
 
 	return 0;
 }
-- 
1.9.1

[PATCH 2/3] ARC: intc: No need to clear IRQ_NOAUTOEN

[Vineet Gupta]

arc_request_percpu_irq() is called by all cores to request/enable percpu
irq. It has some "prep" calls needed by genirq:
 - setup percpu devid
 - disable IRQ_NOAUTOEN

However given that enable_percpu_irq() is called enayways, latter can be
avoided.

We are now left with irq_set_percpu_devid() quirk and that too for
ARCompact builds only, since previous patch updated ARCv2 intc to do this
in the "right" place, i.e. irq map function.

By next release, this will ultimately be fixed for ARCompact as well.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/kernel/irq.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arc/kernel/irq.c b/arch/arc/kernel/irq.c
index 2ee226546c6a..d736678d2724 100644
--- a/arch/arc/kernel/irq.c
+++ b/arch/arc/kernel/irq.c
@@ -60,14 +60,17 @@ void arc_request_percpu_irq(int irq, int cpu,
 	if (!cpu) {
 		int rc;
 
+#ifdef CONFIG_ISA_ARCOMPACT
 		/*
-		 * These 2 calls are essential to making percpu IRQ APIs work
-		 * Ideally these details could be hidden in irq chip map function
-		 * but the issue is IPIs IRQs being static (non-DT) and platform
-		 * specific, so we can't identify them there.
+		 * A subsequent request_percpu_irq() fails if percpu_devid is
+		 * not set. That in turns sets NOAUTOEN, meaning each core needs
+		 * to call enable_percpu_irq()
+		 *
+		 * For ARCv2, this is done in irq map function since we know
+		 * which irqs are strictly per cpu
 		 */
 		irq_set_percpu_devid(irq);
-		irq_modify_status(irq, IRQ_NOAUTOEN, 0);  /* @irq, @clr, @set */
+#endif
 
 		rc = request_percpu_irq(irq, isr, irq_nm, percpu_dev);
 		if (rc)
-- 
1.9.1

[PATCH 3/3] ARCv2: perf: Ensure perf intr gets enabled on all cores

[Vineet Gupta]

This was the second perf intr issue

perf sampling on multicore requires intr to be enabled on all cores.
ARC perf probe code used helper arc_request_percpu_irq() which calls
 - request_percpu_irq() on core0
 - enable_percpu_irq() on all all cores (including core0)

genirq requires that request be made ahead of enable call.
However if perf probe happened on non core0 (observed on a 3.18 kernel),
enable would get called ahead of request, failing obviously and
rendering perf intr disabled on all such cores

[   11.120000] 1 ARC perf       : 8 counters (48 bits), 113 conditions, [overflow IRQ support]
[   11.130000] 1 -----> enable_percpu_irq() IRQ 20 failed
[   11.140000] 3 -----> enable_percpu_irq() IRQ 20 failed
[   11.140000] 2 -----> enable_percpu_irq() IRQ 20 failed
[   11.140000] 0 =====> request_percpu_irq() IRQ 20
[   11.140000] 0 -----> enable_percpu_irq() IRQ 20

Fix this fragility, by calling request_percpu_irq() on whatever core
calls probe (there is no requirement on which core calls this anyways)
and then calling enable on each cores.

Interestingly this started as invesigation of STAR 9000838902:
"sporadically IRQs enabled on perf prob"

which was about occassional boot spew as request_percpu_irq got called
non-locally (from an IPI), and re-enabled interrupts in following path
proc_mkdir ->  spin_unlock_irq()

which the irq work code didn't like.

| ARC perf     : 8 counters (48 bits), 113 conditions, [overflow IRQ support]
|
| BUG: failure at ../kernel/irq_work.c:135/irq_work_run_list()!
| CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.10-01127-g285efb8e66d1 #2
|
| Stack Trace:
|  arc_unwind_core.constprop.1+0x94/0x104
|  dump_stack+0x62/0x98
|  irq_work_run_list+0xb0/0xb4
|  irq_work_run+0x22/0x3c
|  do_IPI+0x74/0x9c
|  handle_irq_event_percpu+0x34/0x164
|  handle_percpu_irq+0x58/0x78
|  generic_handle_irq+0x1e/0x2c
|  arch_do_IRQ+0x3c/0x60
|  ret_from_exception+0x0/0x8

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/kernel/perf_event.c | 32 +++++++++-----------------------
 1 file changed, 9 insertions(+), 23 deletions(-)

diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 0c08bb1ce15a..8b134cfe5e1f 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -428,12 +428,11 @@ static irqreturn_t arc_pmu_intr(int irq, void *dev)
 
 #endif /* CONFIG_ISA_ARCV2 */
 
-void arc_cpu_pmu_irq_init(void)
+static void arc_cpu_pmu_irq_init(void *data)
 {
-	struct arc_pmu_cpu *pmu_cpu = this_cpu_ptr(&arc_pmu_cpu);
+	int irq = *(int *)data;
 
-	arc_request_percpu_irq(arc_pmu->irq, smp_processor_id(), arc_pmu_intr,
-			       "ARC perf counters", pmu_cpu);
+	enable_percpu_irq(irq, IRQ_TYPE_NONE);
 
 	/* Clear all pending interrupt flags */
 	write_aux_reg(ARC_REG_PCT_INT_ACT, 0xffffffff);
@@ -515,7 +514,6 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 
 	if (has_interrupts) {
 		int irq = platform_get_irq(pdev, 0);
-		unsigned long flags;
 
 		if (irq < 0) {
 			pr_err("Cannot get IRQ number for the platform\n");
@@ -524,24 +522,12 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 
 		arc_pmu->irq = irq;
 
-		/*
-		 * arc_cpu_pmu_irq_init() needs to be called on all cores for
-		 * their respective local PMU.
-		 * However we use opencoded on_each_cpu() to ensure it is called
-		 * on core0 first, so that arc_request_percpu_irq() sets up
-		 * AUTOEN etc. Otherwise enable_percpu_irq() fails to enable
-		 * perf IRQ on non master cores.
-		 * see arc_request_percpu_irq()
-		 */
-		preempt_disable();
-		local_irq_save(flags);
-		arc_cpu_pmu_irq_init();
-		local_irq_restore(flags);
-		smp_call_function((smp_call_func_t)arc_cpu_pmu_irq_init, 0, 1);
-		preempt_enable();
-
-		/* Clean all pending interrupt flags */
-		write_aux_reg(ARC_REG_PCT_INT_ACT, 0xffffffff);
+		/* intc map function ensures irq_set_percpu_devid() called */
+		request_percpu_irq(irq, arc_pmu_intr, "ARC perf counters",
+				   this_cpu_ptr(&arc_pmu_cpu));
+
+		on_each_cpu(arc_cpu_pmu_irq_init, &irq, 1);
+
 	} else
 		arc_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 
-- 
1.9.1