x86/apic: Avoid useless scanning thru a cpumask in assign_irq_vector()

In case of static vector allocation domains (i.e. flat) if all
vector numbers are exhausted, an attempt to assign a new vector
will lead to useless scans through all CPUs in the cpumask, even
though it is known that each new pass would fail. Make this
corner case less painful by letting report whether the vector
allocation domain depends on passed arguments or not and stop
scanning early.

The same could have been achived by introducing a static flag to
the apic operations. But let's allow vector_allocation_domain()
have more intelligence here and decide dynamically, in case we
would need it in the future.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/20120607131542.GE4759@dhcp-26-207.brq.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index feb2dbdae9ecebec051160415f415970f8e9ab9c..e3fecd50d5ca8365683c6cff1bb1d082f0dd496f 100644 (file)
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -306,7 +306,7 @@ struct apic {
        unsigned long (*check_apicid_used)(physid_mask_t *map, int apicid);
        unsigned long (*check_apicid_present)(int apicid);
 
-       void (*vector_allocation_domain)(int cpu, struct cpumask *retmask);
+       bool (*vector_allocation_domain)(int cpu, struct cpumask *retmask);
        void (*init_apic_ldr)(void);
 
        void (*ioapic_phys_id_map)(physid_mask_t *phys_map, physid_mask_t *retmap);
@@ -615,7 +615,7 @@ extern unsigned int
 default_cpu_mask_to_apicid_and(const struct cpumask *cpumask,
                               const struct cpumask *andmask);
 
-static inline void
+static inline bool
 flat_vector_allocation_domain(int cpu, struct cpumask *retmask)
 {
        /* Careful. Some cpus do not strictly honor the set of cpus
@@ -628,12 +628,14 @@ flat_vector_allocation_domain(int cpu, struct cpumask *retmask)
         */
        cpumask_clear(retmask);
        cpumask_bits(retmask)[0] = APIC_ALL_CPUS;
+       return false;
 }
 
-static inline void
+static inline bool
 default_vector_allocation_domain(int cpu, struct cpumask *retmask)
 {
        cpumask_copy(retmask, cpumask_of(cpu));
+       return true;
 }
 
 static inline unsigned long default_check_apicid_used(physid_mask_t *map, int apicid)

diff --git a/arch/x86/kernel/apic/apic_noop.c b/arch/x86/kernel/apic/apic_noop.c
index 3e43cf52893920e880d30ce427cbe329aecf2d0a..ac9edf247b15c98f390ffa3d92cf156de1f80d4b 100644 (file)
--- a/arch/x86/kernel/apic/apic_noop.c
+++ b/arch/x86/kernel/apic/apic_noop.c
@@ -100,11 +100,12 @@ static unsigned long noop_check_apicid_present(int bit)
        return physid_isset(bit, phys_cpu_present_map);
 }
 
-static void noop_vector_allocation_domain(int cpu, struct cpumask *retmask)
+static bool noop_vector_allocation_domain(int cpu, struct cpumask *retmask)
 {
        if (cpu != 0)
                pr_warning("APIC: Vector allocated for non-BSP cpu\n");
        cpumask_copy(retmask, cpumask_of(cpu));
+       return true;
 }
 
 static u32 noop_apic_read(u32 reg)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 05af3d341aaa6810beb4f11cd77ee644b0bdc17e..4061a7dee5c9e69cd932d08b6d9b470e65db8bdd 100644 (file)
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1137,8 +1137,9 @@ __assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
        for_each_cpu_and(cpu, mask, cpu_online_mask) {
                int new_cpu;
                int vector, offset;
+               bool more_domains;
 
-               apic->vector_allocation_domain(cpu, tmp_mask);
+               more_domains = apic->vector_allocation_domain(cpu, tmp_mask);
 
                if (cpumask_subset(tmp_mask, cfg->domain)) {
                        free_cpumask_var(tmp_mask);
@@ -1153,8 +1154,13 @@ next:
                        offset = (offset + 1) % 16;
                        vector = FIRST_EXTERNAL_VECTOR + offset;
                }
-               if (unlikely(current_vector == vector))
-                       continue;
+
+               if (unlikely(current_vector == vector)) {
+                       if (more_domains)
+                               continue;
+                       else
+                               break;
+               }
 
                if (test_bit(vector, used_vectors))
                        goto next;