Hi Marc,
On 2019/6/12 1:03, Marc Zyngier wrote:
On a successful translation, preserve the parameters in the LPI
translation cache. Each translation is reusing the last slot
in the list, naturally evincting the least recently used entry.
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
virt/kvm/arm/vgic/vgic-its.c | 86 ++++++++++++++++++++++++++++++++++++
1 file changed, 86 insertions(+)
diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 0aa0cbbc3af6..62932458476a 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -546,6 +546,90 @@ static unsigned long vgic_mmio_read_its_idregs(struct kvm *kvm,
return 0;
}
+static struct vgic_irq *__vgic_its_check_cache(struct vgic_dist *dist,
+ phys_addr_t db,
+ u32 devid, u32 eventid)
+{
+ struct vgic_translation_cache_entry *cte;
+ struct vgic_irq *irq = NULL;
+
+ list_for_each_entry(cte, &dist->lpi_translation_cache, entry) {
+ /*
+ * If we hit a NULL entry, there is nothing after this
+ * point.
+ */
+ if (!cte->irq)
+ break;
+
+ if (cte->db == db &&
+ cte->devid == devid &&
+ cte->eventid == eventid) {
+ /*
+ * Move this entry to the head, as it is the
+ * most recently used.
+ */
+ list_move(&cte->entry, &dist->lpi_translation_cache);
Only for performance reasons: if we hit at the "head" of the list, we
don't need to do a list_move().
In our tests, we found that a single list_move() takes nearly (sometimes
even more than) one microsecond, for some unknown reason...
Thanks,
zenghui
+ irq = cte->irq;
+ break;
+ }
+ }
+
+ return irq;
+}
+
+static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
+ u32 devid, u32 eventid,
+ struct vgic_irq *irq)
+{
+ struct vgic_dist *dist = &kvm->arch.vgic;
+ struct vgic_translation_cache_entry *cte;
+ unsigned long flags;
+ phys_addr_t db;
+
+ /* Do not cache a directly injected interrupt */
+ if (irq->hw)
+ return;
+
+ raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
+
+ if (unlikely(list_empty(&dist->lpi_translation_cache)))
+ goto out;
+
+ /*
+ * We could have raced with another CPU caching the same
+ * translation behind our back, so let's check it is not in
+ * already
+ */
+ db = its->vgic_its_base + GITS_TRANSLATER;
+ if (__vgic_its_check_cache(dist, db, devid, eventid))
+ goto out;
+
+ /* Always reuse the last entry (LRU policy) */
+ cte = list_last_entry(&dist->lpi_translation_cache,
+ typeof(*cte), entry);
+
+ /*
+ * Caching the translation implies having an extra reference
+ * to the interrupt, so drop the potential reference on what
+ * was in the cache, and increment it on the new interrupt.
+ */
+ if (cte->irq)
+ __vgic_put_lpi_locked(kvm, cte->irq);
+
+ vgic_get_irq_kref(irq);
+
+ cte->db = db;
+ cte->devid = devid;
+ cte->eventid = eventid;
+ cte->irq = irq;
+
+ /* Move the new translation to the head of the list */
+ list_move(&cte->entry, &dist->lpi_translation_cache);
+
+out:
+ raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+}
+
void vgic_its_invalidate_cache(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
@@ -589,6 +673,8 @@ int vgic_its_resolve_lpi(struct kvm *kvm, struct vgic_its *its,
if (!vcpu->arch.vgic_cpu.lpis_enabled)
return -EBUSY;
+ vgic_its_cache_translation(kvm, its, devid, eventid, ite->irq);
+
*irq = ite->irq;
return 0;
}
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