[v1,01/14] genirq: Provide new interfaces for affinity hints

Message ID 20210617182242.8637-2-nitesh@redhat.com
State Superseded
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Series
  • [v1,01/14] genirq: Provide new interfaces for affinity hints
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Commit Message

Nitesh Narayan Lal June 17, 2021, 6:22 p.m.
From: Thomas Gleixner <tglx@linutronix.de>

The discussion about removing the side effect of irq_set_affinity_hint() of
actually applying the cpumask (if not NULL) as affinity to the interrupt,
unearthed a few unpleasantries:

  1) The modular perf drivers rely on the current behaviour for the very
     wrong reasons.

  2) While none of the other drivers prevents user space from changing
     the affinity, a cursorily inspection shows that there are at least
     expectations in some drivers.

#1 needs to be cleaned up anyway, so that's not a problem

#2 might result in subtle regressions especially when irqbalanced (which
   nowadays ignores the affinity hint) is disabled.

Provide new interfaces:

  irq_update_affinity_hint()  - Only sets the affinity hint pointer
  irq_set_affinity_and_hint() - Set the pointer and apply the affinity to
                                the interrupt

Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and
document it to be phased out.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com
---
 include/linux/interrupt.h | 41 ++++++++++++++++++++++++++++++++++++++-
 kernel/irq/manage.c       |  8 ++++----
 2 files changed, 44 insertions(+), 5 deletions(-)

Comments

Nitesh Lal June 25, 2021, 5:52 p.m. | #1
On Thu, Jun 17, 2021 at 2:23 PM Nitesh Narayan Lal <nitesh@redhat.com> wrote:
>

> From: Thomas Gleixner <tglx@linutronix.de>

>

> The discussion about removing the side effect of irq_set_affinity_hint() of

> actually applying the cpumask (if not NULL) as affinity to the interrupt,

> unearthed a few unpleasantries:

>

>   1) The modular perf drivers rely on the current behaviour for the very

>      wrong reasons.

>

>   2) While none of the other drivers prevents user space from changing

>      the affinity, a cursorily inspection shows that there are at least

>      expectations in some drivers.

>

> #1 needs to be cleaned up anyway, so that's not a problem

>

> #2 might result in subtle regressions especially when irqbalanced (which

>    nowadays ignores the affinity hint) is disabled.

>

> Provide new interfaces:

>

>   irq_update_affinity_hint()  - Only sets the affinity hint pointer

>   irq_set_affinity_and_hint() - Set the pointer and apply the affinity to

>                                 the interrupt

>

> Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and

> document it to be phased out.

>

> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>

> Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com

> ---

>  include/linux/interrupt.h | 41 ++++++++++++++++++++++++++++++++++++++-

>  kernel/irq/manage.c       |  8 ++++----

>  2 files changed, 44 insertions(+), 5 deletions(-)

>

> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h

> index 2ed65b01c961..4ca491a76033 100644

> --- a/include/linux/interrupt.h

> +++ b/include/linux/interrupt.h

> @@ -328,7 +328,46 @@ extern int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask);

>  extern int irq_can_set_affinity(unsigned int irq);

>  extern int irq_select_affinity(unsigned int irq);

>

> -extern int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m);

> +extern int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,

> +                                    bool setaffinity);

> +

> +/**

> + * irq_update_affinity_hint - Update the affinity hint

> + * @irq:       Interrupt to update

> + * @cpumask:   cpumask pointer (NULL to clear the hint)

> + *

> + * Updates the affinity hint, but does not change the affinity of the interrupt.

> + */

> +static inline int

> +irq_update_affinity_hint(unsigned int irq, const struct cpumask *m)

> +{

> +       return __irq_apply_affinity_hint(irq, m, false);

> +}

> +

> +/**

> + * irq_set_affinity_and_hint - Update the affinity hint and apply the provided

> + *                          cpumask to the interrupt

> + * @irq:       Interrupt to update

> + * @cpumask:   cpumask pointer (NULL to clear the hint)

> + *

> + * Updates the affinity hint and if @cpumask is not NULL it applies it as

> + * the affinity of that interrupt.

> + */

> +static inline int

> +irq_set_affinity_and_hint(unsigned int irq, const struct cpumask *m)

> +{

> +       return __irq_apply_affinity_hint(irq, m, true);

> +}

> +

> +/*

> + * Deprecated. Use irq_update_affinity_hint() or irq_set_affinity_and_hint()

> + * instead.

> + */

> +static inline int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)

> +{

> +       return irq_set_affinity_and_hint(irq, m);

> +}

> +

>  extern int irq_update_affinity_desc(unsigned int irq,

>                                     struct irq_affinity_desc *affinity);

>

> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c

> index ef30b4762947..837b63e63111 100644

> --- a/kernel/irq/manage.c

> +++ b/kernel/irq/manage.c

> @@ -487,7 +487,8 @@ int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask)

>  }

>  EXPORT_SYMBOL_GPL(irq_force_affinity);

>

> -int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)

> +int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,

> +                             bool setaffinity)

>  {

>         unsigned long flags;

>         struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);

> @@ -496,12 +497,11 @@ int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)

>                 return -EINVAL;

>         desc->affinity_hint = m;

>         irq_put_desc_unlock(desc, flags);

> -       /* set the initial affinity to prevent every interrupt being on CPU0 */

> -       if (m)

> +       if (m && setaffinity)

>                 __irq_set_affinity(irq, m, false);

>         return 0;

>  }

> -EXPORT_SYMBOL_GPL(irq_set_affinity_hint);

> +EXPORT_SYMBOL_GPL(__irq_apply_affinity_hint);

>

>  static void irq_affinity_notify(struct work_struct *work)

>  {

> --

> 2.27.0

>


It turns out that this patch has an issue. The new interfaces are not
added under the #ifdef (CONFIG_SMP)'s else section.
I will fix it and send a v2 with other changes.


--
Thanks

Nitesh

Patch

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2ed65b01c961..4ca491a76033 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -328,7 +328,46 @@  extern int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask);
 extern int irq_can_set_affinity(unsigned int irq);
 extern int irq_select_affinity(unsigned int irq);
 
-extern int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m);
+extern int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
+				     bool setaffinity);
+
+/**
+ * irq_update_affinity_hint - Update the affinity hint
+ * @irq:	Interrupt to update
+ * @cpumask:	cpumask pointer (NULL to clear the hint)
+ *
+ * Updates the affinity hint, but does not change the affinity of the interrupt.
+ */
+static inline int
+irq_update_affinity_hint(unsigned int irq, const struct cpumask *m)
+{
+	return __irq_apply_affinity_hint(irq, m, false);
+}
+
+/**
+ * irq_set_affinity_and_hint - Update the affinity hint and apply the provided
+ *			     cpumask to the interrupt
+ * @irq:	Interrupt to update
+ * @cpumask:	cpumask pointer (NULL to clear the hint)
+ *
+ * Updates the affinity hint and if @cpumask is not NULL it applies it as
+ * the affinity of that interrupt.
+ */
+static inline int
+irq_set_affinity_and_hint(unsigned int irq, const struct cpumask *m)
+{
+	return __irq_apply_affinity_hint(irq, m, true);
+}
+
+/*
+ * Deprecated. Use irq_update_affinity_hint() or irq_set_affinity_and_hint()
+ * instead.
+ */
+static inline int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
+{
+	return irq_set_affinity_and_hint(irq, m);
+}
+
 extern int irq_update_affinity_desc(unsigned int irq,
 				    struct irq_affinity_desc *affinity);
 
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index ef30b4762947..837b63e63111 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -487,7 +487,8 @@  int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask)
 }
 EXPORT_SYMBOL_GPL(irq_force_affinity);
 
-int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
+int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
+			      bool setaffinity)
 {
 	unsigned long flags;
 	struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
@@ -496,12 +497,11 @@  int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
 		return -EINVAL;
 	desc->affinity_hint = m;
 	irq_put_desc_unlock(desc, flags);
-	/* set the initial affinity to prevent every interrupt being on CPU0 */
-	if (m)
+	if (m && setaffinity)
 		__irq_set_affinity(irq, m, false);
 	return 0;
 }
-EXPORT_SYMBOL_GPL(irq_set_affinity_hint);
+EXPORT_SYMBOL_GPL(__irq_apply_affinity_hint);
 
 static void irq_affinity_notify(struct work_struct *work)
 {