Re: [PATCH v6 01/29] irq/matrix: Expose functions to allocate the best CPU for new vectors

2022-05-11 Thread Ricardo Neri 
On Fri, May 06, 2022 at 09:48:28PM +0200, Thomas Gleixner wrote:
> Ricardo,

Thank you very much for your feedback Thomas! I am sorry for my late reply, I
had been out of office.

> 
> On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
> > Certain types of interrupts, such as NMI, do not have an associated vector.
> > They, however, target specific CPUs. Thus, when assigning the destination
> > CPU, it is beneficial to select the one with the lowest number of
> > vectors.
> 
> Why is that beneficial especially in the context of a NMI watchdog which
> then broadcasts the NMI to all other CPUs?

My intent was not the NMI watchdog specifically but potential use cases that do
not involve NMI broadcasts. If the NMI targets a single CPU, it is best to
select the CPU with the lowest vector allocation count.

> 
> That's wishful thinking perhaps, but I don't see any benefit at all.
> 
> > Prepend the functions matrix_find_best_cpu_managed() and
> > matrix_find_best_cpu_managed()
> 
> The same function prepended twice becomes two functions :)
> 

Sorry, I missed this.

> > with the irq_ prefix and expose them for
> > IRQ controllers to use when allocating and activating vector-less IRQs.
> 
> There is no such thing like a vectorless IRQ. NMIs have a vector. Can we
> please describe facts and not pulled out of thin air concepts which do
> not exist?

Thank you for the clarification. I see your point. I wrote this patch because
maskable interrupts and NMIs have different entry points. As you state,
however, the also have a vector.

I can drop this patch.

BR,
Ricardo

> 
> Thanks,
> 
> tglx
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Re: [PATCH v6 01/29] irq/matrix: Expose functions to allocate the best CPU for new vectors

2022-05-06 Thread Thomas Gleixner 
Ricardo,

On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
> Certain types of interrupts, such as NMI, do not have an associated vector.
> They, however, target specific CPUs. Thus, when assigning the destination
> CPU, it is beneficial to select the one with the lowest number of
> vectors.

Why is that beneficial especially in the context of a NMI watchdog which
then broadcasts the NMI to all other CPUs?

That's wishful thinking perhaps, but I don't see any benefit at all.

> Prepend the functions matrix_find_best_cpu_managed() and
> matrix_find_best_cpu_managed()

The same function prepended twice becomes two functions :)

> with the irq_ prefix and expose them for
> IRQ controllers to use when allocating and activating vector-less IRQs.

There is no such thing like a vectorless IRQ. NMIs have a vector. Can we
please describe facts and not pulled out of thin air concepts which do
not exist?

Thanks,

tglx
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[PATCH v6 01/29] irq/matrix: Expose functions to allocate the best CPU for new vectors

2022-05-05 Thread Ricardo Neri 
Certain types of interrupts, such as NMI, do not have an associated vector.
They, however, target specific CPUs. Thus, when assigning the destination
CPU, it is beneficial to select the one with the lowest number of vectors.
Prepend the functions matrix_find_best_cpu_managed() and
matrix_find_best_cpu_managed() with the irq_ prefix and expose them for
IRQ controllers to use when allocating and activating vector-less IRQs.

Cc: Andi Kleen 
Cc: "Ravi V. Shankar" 
Cc: Stephane Eranian 
Cc: iommu@lists.linux-foundation.org
Cc: linuxppc-...@lists.ozlabs.org
Cc: x...@kernel.org
Reviewed-by: Tony Luck 
Signed-off-by: Ricardo Neri 
---
Changes since v5:
 * Introduced this patch.

Changes since v4:
 * N/A

Changes since v3:
 * N/A

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---
 include/linux/irq.h |  4 
 kernel/irq/matrix.c | 32 +++-
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index f92788ccdba2..9e674e73d295 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -1223,6 +1223,10 @@ struct irq_matrix *irq_alloc_matrix(unsigned int 
matrix_bits,
 void irq_matrix_online(struct irq_matrix *m);
 void irq_matrix_offline(struct irq_matrix *m);
 void irq_matrix_assign_system(struct irq_matrix *m, unsigned int bit, bool 
replace);
+unsigned int irq_matrix_find_best_cpu(struct irq_matrix *m,
+ const struct cpumask *msk);
+unsigned int irq_matrix_find_best_cpu_managed(struct irq_matrix *m,
+ const struct cpumask *msk);
 int irq_matrix_reserve_managed(struct irq_matrix *m, const struct cpumask 
*msk);
 void irq_matrix_remove_managed(struct irq_matrix *m, const struct cpumask 
*msk);
 int irq_matrix_alloc_managed(struct irq_matrix *m, const struct cpumask *msk,
diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c
index 1698e77645ac..810479f608f4 100644
--- a/kernel/irq/matrix.c
+++ b/kernel/irq/matrix.c
@@ -125,9 +125,16 @@ static unsigned int matrix_alloc_area(struct irq_matrix 
*m, struct cpumap *cm,
return area;
 }
 
-/* Find the best CPU which has the lowest vector allocation count */
-static unsigned int matrix_find_best_cpu(struct irq_matrix *m,
-   const struct cpumask *msk)
+/**
+ * irq_matrix_find_best_cpu() - Find the best CPU for an IRQ
+ * @m: Matrix pointer
+ * @msk:   On which CPUs the search will be performed
+ *
+ * Find the best CPU which has the lowest vector allocation count
+ * Returns: The best CPU to use
+ */
+unsigned int irq_matrix_find_best_cpu(struct irq_matrix *m,
+ const struct cpumask *msk)
 {
unsigned int cpu, best_cpu, maxavl = 0;
struct cpumap *cm;
@@ -146,9 +153,16 @@ static unsigned int matrix_find_best_cpu(struct irq_matrix 
*m,
return best_cpu;
 }
 
-/* Find the best CPU which has the lowest number of managed IRQs allocated */
-static unsigned int matrix_find_best_cpu_managed(struct irq_matrix *m,
-   const struct cpumask *msk)
+/**
+ * irq_matrix_find_best_cpu_managed() - Find the best CPU for a managed IRQ
+ * @m: Matrix pointer
+ * @msk:   On which CPUs the search will be performed
+ *
+ * Find the best CPU which has the lowest number of managed IRQs allocated
+ * Returns: The best CPU to use
+ */
+unsigned int irq_matrix_find_best_cpu_managed(struct irq_matrix *m,
+ const struct cpumask *msk)
 {
unsigned int cpu, best_cpu, allocated = UINT_MAX;
struct cpumap *cm;
@@ -292,7 +306,7 @@ int irq_matrix_alloc_managed(struct irq_matrix *m, const 
struct cpumask *msk,
if (cpumask_empty(msk))
return -EINVAL;
 
-   cpu = matrix_find_best_cpu_managed(m, msk);
+   cpu = irq_matrix_find_best_cpu_managed(m, msk);
if (cpu == UINT_MAX)
return -ENOSPC;
 
@@ -381,13 +395,13 @@ int irq_matrix_alloc(struct irq_matrix *m, const struct 
cpumask *msk,
struct cpumap *cm;
 
/*
-* Not required in theory, but matrix_find_best_cpu() uses
+* Not required in theory, but irq_matrix_find_best_cpu() uses
 * for_each_cpu() which ignores the cpumask on UP .
 */
if (cpumask_empty(msk))
return -EINVAL;
 
-   cpu = matrix_find_best_cpu(m, msk);
+   cpu = irq_matrix_find_best_cpu(m, msk);
if (cpu == UINT_MAX)
return -ENOSPC;
 
-- 
2.17.1

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