[PATCH 1/4] hw/nvme: avoid unnecessary call to irq (de)assertion functions

[Jinhao Fan]

nvme_irq_assert() only does useful work when cq->irq_enabled is true.
nvme_irq_deassert() only works for pin-based interrupts. Avoid calls
into these functions if we are sure they will not do useful work.

This will be most useful when we use eventfd to send interrupts. We
can avoid the unnecessary overhead of signalling eventfd.

Signed-off-by: Jinhao Fan <fanjinhao21s@ict.ac.cn>
---
 hw/nvme/ctrl.c | 40 ++++++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index 87aeba0564..bd3350d7e0 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -1377,11 +1377,13 @@ static void nvme_post_cqes(void *opaque)
         QTAILQ_INSERT_TAIL(&sq->req_list, req, entry);
     }
     if (cq->tail != cq->head) {
-        if (cq->irq_enabled && !pending) {
-            n->cq_pending++;
-        }
+        if (cq->irq_enabled) {
+            if (!pending) {
+                n->cq_pending++;
+            }
 
-        nvme_irq_assert(n, cq);
+            nvme_irq_assert(n, cq);
+        }
     }
 }
 
@@ -4244,12 +4246,11 @@ static void nvme_cq_notifier(EventNotifier *e)
 
     nvme_update_cq_head(cq);
 
-    if (cq->tail == cq->head) {
-        if (cq->irq_enabled) {
-            n->cq_pending--;
+    if (cq->irq_enabled && cq->tail == cq->head) {
+        n->cq_pending--;
+        if (!msix_enabled(&n->parent_obj)) {
+            nvme_irq_deassert(n, cq);
         }
-
-        nvme_irq_deassert(n, cq);
     }
 
     nvme_post_cqes(cq);
@@ -4730,11 +4731,15 @@ static uint16_t nvme_del_cq(NvmeCtrl *n, NvmeRequest 
*req)
         return NVME_INVALID_QUEUE_DEL;
     }
 
-    if (cq->irq_enabled && cq->tail != cq->head) {
-        n->cq_pending--;
-    }
+    if (cq->irq_enabled) {
+        if (cq->tail != cq->head) {
+            n->cq_pending--;
+        }
 
-    nvme_irq_deassert(n, cq);
+        if (!msix_enabled(&n->parent_obj)) {
+            nvme_irq_deassert(n, cq);
+        }
+    }
     trace_pci_nvme_del_cq(qid);
     nvme_free_cq(cq, n);
     return NVME_SUCCESS;
@@ -6918,12 +6923,11 @@ static void nvme_process_db(NvmeCtrl *n, hwaddr addr, 
int val)
             timer_mod(cq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);
         }
 
-        if (cq->tail == cq->head) {
-            if (cq->irq_enabled) {
-                n->cq_pending--;
+        if (cq->irq_enabled && cq->tail == cq->head) {
+            n->cq_pending--;
+            if (!msix_enabled(&n->parent_obj)) {
+                nvme_irq_deassert(n, cq);
             }
-
-            nvme_irq_deassert(n, cq);
         }
     } else {
         /* Submission queue doorbell write */
-- 
2.25.1