[PATCH v1 3/6] irqchip/gic-v3: support SGI broadcast

[Yu Zhao]

GIC v3 and later support SGI broadcast, i.e., the mode that routes
interrupts to all PEs in the system excluding the local CPU.

Supporting this mode can avoid looping through all the remote CPUs
when broadcasting SGIs, especially for systems with 200+ CPUs. The
performance improvement can be measured with the rest of this series
booted with "hugetlb_free_vmemmap=on irqchip.gicv3_pseudo_nmi=1":

  cd /sys/kernel/mm/hugepages/
  echo 600 >hugepages-1048576kB/nr_hugepages
  echo 2048kB >hugepages-1048576kB/demote_size
  perf record -g -- bash -c "echo 600 >hugepages-1048576kB/demote"

         gic_ipi_send_mask()  bash sys time
Before:  38.14%               0m10.513s
After:    0.20%               0m5.132s

Signed-off-by: Yu Zhao <yuzhao at google.com>
---
 drivers/irqchip/irq-gic-v3.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index ce87205e3e82..42c39385e1b9 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -1394,9 +1394,20 @@ static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
 	gic_write_sgi1r(val);
 }
 
+static void gic_broadcast_sgi(unsigned int irq)
+{
+	u64 val;
+
+	val = BIT(ICC_SGI1R_IRQ_ROUTING_MODE_BIT) | (irq << ICC_SGI1R_SGI_ID_SHIFT);
+
+	pr_devel("CPU %d: broadcasting SGI %u\n", smp_processor_id(), irq);
+	gic_write_sgi1r(val);
+}
+
 static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
 {
 	int cpu;
+	cpumask_t broadcast;
 
 	if (WARN_ON(d->hwirq >= 16))
 		return;
@@ -1407,6 +1418,13 @@ static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
 	 */
 	dsb(ishst);
 
+	cpumask_copy(&broadcast, cpu_present_mask);
+	cpumask_clear_cpu(smp_processor_id(), &broadcast);
+	if (cpumask_equal(&broadcast, mask)) {
+		gic_broadcast_sgi(d->hwirq);
+		goto done;
+	}
+
 	for_each_cpu(cpu, mask) {
 		u64 cluster_id = MPIDR_TO_SGI_CLUSTER_ID(gic_cpu_to_affinity(cpu));
 		u16 tlist;
@@ -1414,7 +1432,7 @@ static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
 		tlist = gic_compute_target_list(&cpu, mask, cluster_id);
 		gic_send_sgi(cluster_id, tlist, d->hwirq);
 	}
-
+done:
 	/* Force the above writes to ICC_SGI1R_EL1 to be executed */
 	isb();
 }
-- 
2.47.0.rc1.288.g06298d1525-goog