Le 06/04/2021 à 11:35, Marc Zyngier a écrit :
irq_linear_revmap() is supposed to be a fast path for domain
lookups, but it only exposes low-level details of the irqdomain
implementation, details which are better kept private.
Can you elaborate with more details ?
The *overhead* between the two is only a function call and
a couple of tests, so it is likely that noone can show any
meaningful difference compared to the cost of taking an
interrupt.
Do you have any measurement ?
Can you make the "likely" a certitude ?
Reimplement irq_linear_revmap() with irq_find_mapping()
in order to preserve source code compatibility, and
rename the internal field for a measure.
This is in complete contradiction with commit https://github.com/torvalds/linux/commit/d3dcb436
At that time, irq_linear_revmap() was less complex than what irq_find_mapping() is today, and
nevertheless it was considered worth restoring in as a fast path. What has changed since then ?
Can you also explain the reason for the renaming of "linear_revmap" into "revmap" ? What is that
"measure" ?
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
include/linux/irqdomain.h | 22 +++++++++-------------
kernel/irq/irqdomain.c | 6 +++---
2 files changed, 12 insertions(+), 16 deletions(-)
diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
index 33cacc8af26d..b9600f24878a 100644
--- a/include/linux/irqdomain.h
+++ b/include/linux/irqdomain.h
@@ -154,9 +154,9 @@ struct irq_domain_chip_generic;
* Revmap data, used internally by irq_domain
* @revmap_direct_max_irq: The largest hwirq that can be set for controllers that
* support direct mapping
- * @revmap_size: Size of the linear map table @linear_revmap[]
+ * @revmap_size: Size of the linear map table @revmap[]
* @revmap_tree: Radix map tree for hwirqs that don't fit in the linear map
- * @linear_revmap: Linear table of hwirq->virq reverse mappings
+ * @revmap: Linear table of hwirq->virq reverse mappings
*/
struct irq_domain {
struct list_head link;
@@ -180,7 +180,7 @@ struct irq_domain {
unsigned int revmap_size;
struct radix_tree_root revmap_tree;
struct mutex revmap_tree_mutex;
- unsigned int linear_revmap[];
+ unsigned int revmap[];
};
/* Irq domain flags */
@@ -396,24 +396,20 @@ static inline unsigned int irq_create_mapping(struct irq_domain *host,
return irq_create_mapping_affinity(host, hwirq, NULL);
}
-
/**
- * irq_linear_revmap() - Find a linux irq from a hw irq number.
+ * irq_find_mapping() - Find a linux irq from a hw irq number.
* @domain: domain owning this hardware interrupt
* @hwirq: hardware irq number in that domain space
- *
- * This is a fast path alternative to irq_find_mapping() that can be
- * called directly by irq controller code to save a handful of
- * instructions. It is always safe to call, but won't find irqs mapped
- * using the radix tree.
*/
+extern unsigned int irq_find_mapping(struct irq_domain *host,
+ irq_hw_number_t hwirq);
+
static inline unsigned int irq_linear_revmap(struct irq_domain *domain,
irq_hw_number_t hwirq)
{
- return hwirq < domain->revmap_size ? domain->linear_revmap[hwirq] : 0;
+ return irq_find_mapping(domain, hwirq);
}
-extern unsigned int irq_find_mapping(struct irq_domain *host,
- irq_hw_number_t hwirq);
+
extern unsigned int irq_create_direct_mapping(struct irq_domain *host);
extern int irq_create_strict_mappings(struct irq_domain *domain,
unsigned int irq_base,
diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index d10ab1d689d5..dfa716305ea9 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -486,7 +486,7 @@ static void irq_domain_clear_mapping(struct irq_domain *domain,
irq_hw_number_t hwirq)
{
if (hwirq < domain->revmap_size) {
- domain->linear_revmap[hwirq] = 0;
+ domain->revmap[hwirq] = 0;
} else {
mutex_lock(&domain->revmap_tree_mutex);
radix_tree_delete(&domain->revmap_tree, hwirq);
@@ -499,7 +499,7 @@ static void irq_domain_set_mapping(struct irq_domain *domain,
struct irq_data *irq_data)
{
if (hwirq < domain->revmap_size) {
- domain->linear_revmap[hwirq] = irq_data->irq;
+ domain->revmap[hwirq] = irq_data->irq;
} else {
mutex_lock(&domain->revmap_tree_mutex);
radix_tree_insert(&domain->revmap_tree, hwirq, irq_data);
@@ -920,7 +920,7 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
/* Check if the hwirq is in the linear revmap. */
if (hwirq < domain->revmap_size)
- return domain->linear_revmap[hwirq];
+ return domain->revmap[hwirq];
rcu_read_lock();
data = radix_tree_lookup(&domain->revmap_tree, hwirq);
