Messages in this thread | | | Subject | Re: [PATCH 1/9] irqdomain: Reimplement irq_linear_revmap() with irq_find_mapping() | From | Christophe Leroy <> | Date | Tue, 6 Apr 2021 13:21:33 +0200 |
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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@kernel.org> > --- > 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); >
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