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Subject[PATCH] x86/irq: Do not check available vectors if no irq to migrate or required slots has been found
Date
A micro optimization to bypass the free vector checking if the current
CPU has no irq to migrate, also breaks the for_each_online_cpu() loop
when the count reaches the required vectors.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.orq>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
arch/x86/kernel/irq.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 4d8183b..f34fe74 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -394,6 +394,9 @@ int check_irq_vectors_for_cpu_disable(void)
!cpumask_subset(&affinity_new, &online_new))
this_count++;
}
+ /* No need to check any further. */
+ if (!this_count)
+ return 0;

count = 0;
for_each_online_cpu(cpu) {
@@ -411,8 +414,10 @@ int check_irq_vectors_for_cpu_disable(void)
for (vector = FIRST_EXTERNAL_VECTOR;
vector < first_system_vector; vector++) {
if (!test_bit(vector, used_vectors) &&
- IS_ERR_OR_NULL(per_cpu(vector_irq, cpu)[vector]))
- count++;
+ IS_ERR_OR_NULL(per_cpu(vector_irq, cpu)[vector])) {
+ if (++count == this_count)
+ return 0;
+ }
}
}

--
2.7.4
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