[PATCH v5 0/5] IRQ affinity support in PLIC driver

[PATCH v5 0/5] IRQ affinity support in PLIC driver

[Anup Patel]

This patchset primarily adds IRQ affinity support in PLIC driver and
other improvements.

It gives mechanism for explicitly route external interrupts to particular
CPUs using smp_affinity attribute of each Linux IRQs. Also, we can now
use IRQ balancer from kernel-space or user-space.

The patchset is tested on QEMU virt machine. It is based on Linux-4.20
and can be found at riscv_plic_irq_affinity_v4 branch of:
https://github.com/avpatel/linux.git

Changes since v4:
 - Use "if (force)" instead of "if (!force)" in PATCH5

Changes since v3:
 - Dropped PATCH2
 - Added PATCH to not inline plic_toggle() and plic_irq_toggle()
 - Moved PATCH3 changes to PATCH6
 - Used WARN_ON_ONCE() instead of WARN_ON() in PATCH5

Changes since v2:
 - Fixed incorrect address of enable registers using sizeof(u32) in PATCH1
 - Retained comment about need for locking in PATCH1
 - Split PATCH2 into two patches
 - Split PATCH3 into two patches
 - Minor fix in commit description of PATCH4

Changes since v1:
 - Removed few whitspace changes from PATCH1
 - Keep use of DEFINE_PER_CPU() as it is

Anup Patel (5):
  irqchip: sifive-plic: Pre-compute context hart base and enable base
  irqchip: sifive-plic: Don't inline plic_toggle() and plic_irq_toggle()
  irqchip: sifive-plic: Add warning in plic_init() if handler already
    present
  irqchip: sifive-plic: Differentiate between PLIC handler and context
  irqchip: sifive-plic: Implement irq_set_affinity() for SMP host

 drivers/irqchip/irq-sifive-plic.c | 110 +++++++++++++++++++-----------
 1 file changed, 71 insertions(+), 39 deletions(-)

-- 
2.17.1


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[PATCH v5 1/5] irqchip: sifive-plic: Pre-compute context hart base and enable base

[Anup Patel]

This patch does following optimizations:
1. Pre-compute hart base for each context handler
2. Pre-compute enable base for each context handler
3. Have enable lock for each context handler instead
of global plic_toggle_lock

Signed-off-by: Anup Patel <anup@brainfault.org>
---
 drivers/irqchip/irq-sifive-plic.c | 47 ++++++++++++++-----------------
 1 file changed, 21 insertions(+), 26 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index 357e9daf94ae..c23a293a2aae 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -59,37 +59,28 @@ static void __iomem *plic_regs;
 
 struct plic_handler {
 	bool			present;
-	int			ctxid;
+	void __iomem		*hart_base;
+	/*
+	 * Protect mask operations on the registers given that we can't
+	 * assume atomic memory operations work on them.
+	 */
+	raw_spinlock_t		enable_lock;
+	void __iomem		*enable_base;
 };
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
 
-static inline void __iomem *plic_hart_offset(int ctxid)
-{
-	return plic_regs + CONTEXT_BASE + ctxid * CONTEXT_PER_HART;
-}
-
-static inline u32 __iomem *plic_enable_base(int ctxid)
-{
-	return plic_regs + ENABLE_BASE + ctxid * ENABLE_PER_HART;
-}
-
-/*
- * Protect mask operations on the registers given that we can't assume that
- * atomic memory operations work on them.
- */
-static DEFINE_RAW_SPINLOCK(plic_toggle_lock);
-
-static inline void plic_toggle(int ctxid, int hwirq, int enable)
+static inline void plic_toggle(struct plic_handler *handler,
+				int hwirq, int enable)
 {
-	u32 __iomem *reg = plic_enable_base(ctxid) + (hwirq / 32);
+	u32 __iomem *reg = handler->enable_base + (hwirq / 32) * sizeof(u32);
 	u32 hwirq_mask = 1 << (hwirq % 32);
 
-	raw_spin_lock(&plic_toggle_lock);
+	raw_spin_lock(&handler->enable_lock);
 	if (enable)
 		writel(readl(reg) | hwirq_mask, reg);
 	else
 		writel(readl(reg) & ~hwirq_mask, reg);
-	raw_spin_unlock(&plic_toggle_lock);
+	raw_spin_unlock(&handler->enable_lock);
 }
 
 static inline void plic_irq_toggle(struct irq_data *d, int enable)
@@ -101,7 +92,7 @@ static inline void plic_irq_toggle(struct irq_data *d, int enable)
 		struct plic_handler *handler = per_cpu_ptr(&plic_handlers, cpu);
 
 		if (handler->present)
-			plic_toggle(handler->ctxid, d->hwirq, enable);
+			plic_toggle(handler, d->hwirq, enable);
 	}
 }
 
@@ -150,7 +141,7 @@ static struct irq_domain *plic_irqdomain;
 static void plic_handle_irq(struct pt_regs *regs)
 {
 	struct plic_handler *handler = this_cpu_ptr(&plic_handlers);
-	void __iomem *claim = plic_hart_offset(handler->ctxid) + CONTEXT_CLAIM;
+	void __iomem *claim = handler->hart_base + CONTEXT_CLAIM;
 	irq_hw_number_t hwirq;
 
 	WARN_ON_ONCE(!handler->present);
@@ -239,12 +230,16 @@ static int __init plic_init(struct device_node *node,
 		cpu = riscv_hartid_to_cpuid(hartid);
 		handler = per_cpu_ptr(&plic_handlers, cpu);
 		handler->present = true;
-		handler->ctxid = i;
+		handler->hart_base =
+			plic_regs + CONTEXT_BASE + i * CONTEXT_PER_HART;
+		raw_spin_lock_init(&handler->enable_lock);
+		handler->enable_base =
+			plic_regs + ENABLE_BASE + i * ENABLE_PER_HART;
 
 		/* priority must be > threshold to trigger an interrupt */
-		writel(0, plic_hart_offset(i) + CONTEXT_THRESHOLD);
+		writel(0, handler->hart_base + CONTEXT_THRESHOLD);
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
-			plic_toggle(i, hwirq, 0);
+			plic_toggle(handler, hwirq, 0);
 		nr_mapped++;
 	}
 
-- 
2.17.1


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[PATCH v5 2/5] irqchip: sifive-plic: Don't inline plic_toggle() and plic_irq_toggle()

[Anup Patel]

The plic_toggle() uses raw_spin_lock() and plic_irq_toggle has a
for loop so both these functions are not suitable for being inline
hence this patch removes the inline keyword.

Signed-off-by: Anup Patel <anup@brainfault.org>
---
 drivers/irqchip/irq-sifive-plic.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index c23a293a2aae..01bbbbffbcae 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -69,8 +69,8 @@ struct plic_handler {
 };
 static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
 
-static inline void plic_toggle(struct plic_handler *handler,
-				int hwirq, int enable)
+static void plic_toggle(struct plic_handler *handler,
+			int hwirq, int enable)
 {
 	u32 __iomem *reg = handler->enable_base + (hwirq / 32) * sizeof(u32);
 	u32 hwirq_mask = 1 << (hwirq % 32);
@@ -83,7 +83,7 @@ static inline void plic_toggle(struct plic_handler *handler,
 	raw_spin_unlock(&handler->enable_lock);
 }
 
-static inline void plic_irq_toggle(struct irq_data *d, int enable)
+static void plic_irq_toggle(struct irq_data *d, int enable)
 {
 	int cpu;
 
-- 
2.17.1


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[PATCH v5 3/5] irqchip: sifive-plic: Add warning in plic_init() if handler already present

[Anup Patel]

We have two enteries (one for M-mode and another for S-mode) in the
interrupts-extended DT property of PLIC DT node for each HART. It is
expected that firmware/bootloader will set M-mode HWIRQ line of each
HART to 0xffffffff (i.e. -1) in interrupts-extended DT property
because Linux runs in S-mode only.

If firmware/bootloader is buggy then it will not correctly update
interrupts-extended DT property which might result in a plic_handler
configured twice. This patch adds a warning in plic_init() if a
plic_handler is already marked present. This warning provides us
a hint about incorrectly updated interrupts-extended DT property.

Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 drivers/irqchip/irq-sifive-plic.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index 01bbbbffbcae..b9a0bcefe426 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -229,6 +229,11 @@ static int __init plic_init(struct device_node *node,
 
 		cpu = riscv_hartid_to_cpuid(hartid);
 		handler = per_cpu_ptr(&plic_handlers, cpu);
+		if (handler->present) {
+			pr_warn("handler already present for context %d.\n", i);
+			continue;
+		}
+
 		handler->present = true;
 		handler->hart_base =
 			plic_regs + CONTEXT_BASE + i * CONTEXT_PER_HART;
-- 
2.17.1


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[PATCH v5 4/5] irqchip: sifive-plic: Differentiate between PLIC handler and context

[Anup Patel]

We explicitly differentiate between PLIC handler and context because
PLIC context is for given mode of HART whereas PLIC handler is per-CPU
software construct meant for handling interrupts from a particular
PLIC context.

To achieve this differentiation, we rename "nr_handlers" to "nr_contexts"
and "nr_mapped" to "nr_handlers" in plic_init().

Signed-off-by: Anup Patel <anup@brainfault.org>
---
 drivers/irqchip/irq-sifive-plic.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index b9a0bcefe426..24c906f4be93 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -177,7 +177,7 @@ static int plic_find_hart_id(struct device_node *node)
 static int __init plic_init(struct device_node *node,
 		struct device_node *parent)
 {
-	int error = 0, nr_handlers, nr_mapped = 0, i;
+	int error = 0, nr_contexts, nr_handlers = 0, i;
 	u32 nr_irqs;
 
 	if (plic_regs) {
@@ -194,10 +194,10 @@ static int __init plic_init(struct device_node *node,
 	if (WARN_ON(!nr_irqs))
 		goto out_iounmap;
 
-	nr_handlers = of_irq_count(node);
-	if (WARN_ON(!nr_handlers))
+	nr_contexts = of_irq_count(node);
+	if (WARN_ON(!nr_contexts))
 		goto out_iounmap;
-	if (WARN_ON(nr_handlers < num_possible_cpus()))
+	if (WARN_ON(nr_contexts < num_possible_cpus()))
 		goto out_iounmap;
 
 	error = -ENOMEM;
@@ -206,7 +206,7 @@ static int __init plic_init(struct device_node *node,
 	if (WARN_ON(!plic_irqdomain))
 		goto out_iounmap;
 
-	for (i = 0; i < nr_handlers; i++) {
+	for (i = 0; i < nr_contexts; i++) {
 		struct of_phandle_args parent;
 		struct plic_handler *handler;
 		irq_hw_number_t hwirq;
@@ -245,11 +245,11 @@ static int __init plic_init(struct device_node *node,
 		writel(0, handler->hart_base + CONTEXT_THRESHOLD);
 		for (hwirq = 1; hwirq <= nr_irqs; hwirq++)
 			plic_toggle(handler, hwirq, 0);
-		nr_mapped++;
+		nr_handlers++;
 	}
 
-	pr_info("mapped %d interrupts to %d (out of %d) handlers.\n",
-		nr_irqs, nr_mapped, nr_handlers);
+	pr_info("mapped %d interrupts with %d handlers for %d contexts.\n",
+		nr_irqs, nr_handlers, nr_contexts);
 	set_handle_irq(plic_handle_irq);
 	return 0;
 
-- 
2.17.1


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[PATCH v5 5/5] irqchip: sifive-plic: Implement irq_set_affinity() for SMP host

[Anup Patel]

Currently on SMP host, all CPUs take external interrupts routed via
PLIC. All CPUs will try to claim a given external interrupt but only
one of them will succeed while other CPUs would simply resume whatever
they were doing before. This means if we have N CPUs then for every
external interrupt N-1 CPUs will always fail to claim it and waste
their CPU time.

Instead of above, external interrupts should be taken by only one CPU
and we should have provision to explicitly specify IRQ affinity from
kernel-space or user-space.

This patch provides irq_set_affinity() implementation for PLIC driver.
It also updates irq_enable() such that PLIC interrupts are only enabled
for one of CPUs specified in IRQ affinity mask.

With this patch in-place, we can change IRQ affinity at any-time from
user-space using procfs.

Example:

/ # cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3
  8:         44          0          0          0  SiFive PLIC   8  virtio0
 10:         48          0          0          0  SiFive PLIC  10  ttyS0
IPI0:        55        663         58        363  Rescheduling interrupts
IPI1:         0          1          3         16  Function call interrupts
/ #
/ #
/ # echo 4 > /proc/irq/10/smp_affinity
/ #
/ # cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3
  8:         45          0          0          0  SiFive PLIC   8  virtio0
 10:        160          0         17          0  SiFive PLIC  10  ttyS0
IPI0:        68        693         77        410  Rescheduling interrupts
IPI1:         0          2          3         16  Function call interrupts

Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 drivers/irqchip/irq-sifive-plic.c | 44 ++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index 24c906f4be93..e04a862c2cfb 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -83,29 +83,58 @@ static void plic_toggle(struct plic_handler *handler,
 	raw_spin_unlock(&handler->enable_lock);
 }
 
-static void plic_irq_toggle(struct irq_data *d, int enable)
+static void plic_irq_toggle(const struct cpumask *mask, int hwirq, int enable)
 {
 	int cpu;
 
-	writel(enable, plic_regs + PRIORITY_BASE + d->hwirq * PRIORITY_PER_ID);
-	for_each_cpu(cpu, irq_data_get_affinity_mask(d)) {
+	writel(enable, plic_regs + PRIORITY_BASE + hwirq * PRIORITY_PER_ID);
+	for_each_cpu(cpu, mask) {
 		struct plic_handler *handler = per_cpu_ptr(&plic_handlers, cpu);
 
 		if (handler->present)
-			plic_toggle(handler, d->hwirq, enable);
+			plic_toggle(handler, hwirq, enable);
 	}
 }
 
 static void plic_irq_enable(struct irq_data *d)
 {
-	plic_irq_toggle(d, 1);
+	unsigned int cpu = cpumask_any_and(irq_data_get_affinity_mask(d),
+					   cpu_online_mask);
+	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
+		return;
+	plic_irq_toggle(cpumask_of(cpu), d->hwirq, 1);
 }
 
 static void plic_irq_disable(struct irq_data *d)
 {
-	plic_irq_toggle(d, 0);
+	plic_irq_toggle(cpu_possible_mask, d->hwirq, 0);
 }
 
+#ifdef CONFIG_SMP
+static int plic_set_affinity(struct irq_data *d,
+			     const struct cpumask *mask_val, bool force)
+{
+	unsigned int cpu;
+
+	if (force)
+		cpu = cpumask_first(mask_val);
+	else
+		cpu = cpumask_any_and(mask_val, cpu_online_mask);
+
+	if (cpu >= nr_cpu_ids)
+		return -EINVAL;
+
+	if (!irqd_irq_disabled(d)) {
+		plic_irq_toggle(cpu_possible_mask, d->hwirq, 0);
+		plic_irq_toggle(cpumask_of(cpu), d->hwirq, 1);
+	}
+
+	irq_data_update_effective_affinity(d, cpumask_of(cpu));
+
+	return IRQ_SET_MASK_OK_DONE;
+}
+#endif
+
 static struct irq_chip plic_chip = {
 	.name		= "SiFive PLIC",
 	/*
@@ -114,6 +143,9 @@ static struct irq_chip plic_chip = {
 	 */
 	.irq_enable	= plic_irq_enable,
 	.irq_disable	= plic_irq_disable,
+#ifdef CONFIG_SMP
+	.irq_set_affinity = plic_set_affinity,
+#endif
 };
 
 static int plic_irqdomain_map(struct irq_domain *d, unsigned int irq,
-- 
2.17.1


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Re: [PATCH v5 2/5] irqchip: sifive-plic: Don't inline plic_toggle() and plic_irq_toggle()

[Christoph Hellwig]

On Sat, Jan 19, 2019 at 11:26:22AM +0530, Anup Patel wrote:
> The plic_toggle() uses raw_spin_lock() and plic_irq_toggle has a
> for loop so both these functions are not suitable for being inline
> hence this patch removes the inline keyword.

I still very much disagree.  Very strongly with the above rationale,
but also (less strongly) with the decision not to inline here.

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Re: [PATCH v5 4/5] irqchip: sifive-plic: Differentiate between PLIC handler and context

[Christoph Hellwig]

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>

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Re: [PATCH v5 1/5] irqchip: sifive-plic: Pre-compute context hart base and enable base

[Christoph Hellwig]

On Sat, Jan 19, 2019 at 11:26:21AM +0530, Anup Patel wrote:
> This patch does following optimizations:
> 1. Pre-compute hart base for each context handler
> 2. Pre-compute enable base for each context handler
> 3. Have enable lock for each context handler instead
> of global plic_toggle_lock
> 
> Signed-off-by: Anup Patel <anup@brainfault.org>
> ---
>  drivers/irqchip/irq-sifive-plic.c | 47 ++++++++++++++-----------------
>  1 file changed, 21 insertions(+), 26 deletions(-)

I don't really see the point, but the code looks clean enough and
removes a few lines, so:

Reviewed-by: Christoph Hellwig <hch@lst.de>

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Re: [PATCH v5 2/5] irqchip: sifive-plic: Don't inline plic_toggle() and plic_irq_toggle()

[Anup Patel]

On Tue, Feb 12, 2019 at 12:39 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Sat, Jan 19, 2019 at 11:26:22AM +0530, Anup Patel wrote:
> > The plic_toggle() uses raw_spin_lock() and plic_irq_toggle has a
> > for loop so both these functions are not suitable for being inline
> > hence this patch removes the inline keyword.
>
> I still very much disagree.  Very strongly with the above rationale,
> but also (less strongly) with the decision not to inline here.

No issues. I will drop this patch since you "very much disagree".

Regards,
Anup

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