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Subject[PATCH 3/4] x86/apic: Introduce the per vector cpumask array
Date
This array is a bitmap for sorting the number of vectors
assigned on each CPU, thus to quickly retrieve the CPU
which have assigned the least amount of vectors, then
choose that CPU as a hint to spread the vectors among
multiple CPUs.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
arch/x86/kernel/apic/vector.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 4ff84c0..b60cc66 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -32,6 +32,16 @@ struct irq_domain *x86_vector_domain;
EXPORT_SYMBOL_GPL(x86_vector_domain);
static DEFINE_RAW_SPINLOCK(vector_lock);
static cpumask_var_t vector_cpumask, vector_searchmask, searched_cpumask;
+/*
+ * vectors_alloc_mask[i] records the CPUs which have assigned i vectors each.
+ * For example, let vectors_alloc_mask[3] = cpumask_or(cpumask_of(8), cpumask_of(9))
+ * which means that:
+ * On CPU8 and CPU9, the number of vectors been assigned is 3.
+ * This bitmap can be used to quickly find out the CPUs who has allocated the least
+ * number of vectors, by checking from vectors_alloc_mask[0] to vectors_alloc_mask[255]
+ * until a non-zero value is found. These CPUs are chosen for vector spreading.
+ */
+static cpumask_var_t vectors_alloc_mask[NR_VECTORS];
static struct irq_chip lapic_controller;
#ifdef CONFIG_X86_IO_APIC
static struct apic_chip_data *legacy_irq_data[NR_IRQS_LEGACY];
@@ -65,6 +75,9 @@ static void update_vectors_alloc(const struct cpumask *mask,
per_cpu(vector_irq, cpu).alloc -= count;
else
continue;
+ /* Update the position for this CPU. */
+ cpumask_clear_cpu(cpu, vectors_alloc_mask[cur_alloc]);
+ cpumask_set_cpu(cpu, vectors_alloc_mask[per_cpu(vector_irq, cpu).alloc]);
}
}

@@ -479,6 +492,25 @@ static void __init init_legacy_irqs(void)
static inline void init_legacy_irqs(void) { }
#endif

+static int __init alloc_assigned_vectors_mask(void)
+{
+ int i, ret;
+
+ for (i = 0; i < NR_VECTORS; i++) {
+ ret = alloc_cpumask_var(&vectors_alloc_mask[i], GFP_KERNEL);
+ if (!ret)
+ goto free_mask;
+ }
+ /* Initially all the CPUs have 0 vector assigned. */
+ cpumask_setall(vectors_alloc_mask[0]);
+ return 0;
+
+ free_mask:
+ while (i--)
+ free_cpumask_var(vectors_alloc_mask[i]);
+ return -ENOMEM;
+}
+
int __init arch_early_irq_init(void)
{
struct fwnode_handle *fn;
@@ -499,6 +531,7 @@ int __init arch_early_irq_init(void)
BUG_ON(!alloc_cpumask_var(&vector_cpumask, GFP_KERNEL));
BUG_ON(!alloc_cpumask_var(&vector_searchmask, GFP_KERNEL));
BUG_ON(!alloc_cpumask_var(&searched_cpumask, GFP_KERNEL));
+ BUG_ON(alloc_assigned_vectors_mask());

return arch_early_ioapic_init();
}
--
2.7.4
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