[PATCH v2 2/3] hw/nvme: use KVM irqfd when available

[Jinhao Fan]

Use KVM's irqfd to send interrupts when possible. This approach is
thread safe. Moreover, it does not have the inter-thread communication
overhead of plain event notifiers since handler callback are called
in the same system call as irqfd write.

Signed-off-by: Jinhao Fan <fanjinhao21s@ict.ac.cn>
---
 hw/nvme/ctrl.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++--
 hw/nvme/nvme.h |  1 +
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index 6ecf6fafd9..74075f782f 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -192,6 +192,7 @@
 #include "qapi/error.h"
 #include "qapi/visitor.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/kvm.h"
 #include "sysemu/block-backend.h"
 #include "sysemu/hostmem.h"
 #include "hw/pci/msix.h"
@@ -1377,8 +1378,26 @@ static void nvme_deassert_notifier_read(EventNotifier *e)
     }
 }
 
+static int nvme_kvm_msix_vector_use(NvmeCtrl *n,
+                                    NvmeCQueue *cq,
+                                    uint32_t vector)
+{
+    int ret;
+
+    KVMRouteChange c = kvm_irqchip_begin_route_changes(kvm_state);
+    ret = kvm_irqchip_add_msi_route(&c, vector, &n->parent_obj);
+    if (ret < 0) {
+        return ret;
+    }
+    kvm_irqchip_commit_route_changes(&c);
+    cq->virq = ret;
+    return 0;
+}
+
 static void nvme_init_irq_notifier(NvmeCtrl *n, NvmeCQueue *cq)
 {
+    bool with_irqfd = msix_enabled(&n->parent_obj) &&
+                      kvm_msi_via_irqfd_enabled();
     int ret;
 
     ret = event_notifier_init(&cq->assert_notifier, 0);
@@ -1386,8 +1405,21 @@ static void nvme_init_irq_notifier(NvmeCtrl *n, 
NvmeCQueue *cq)
         goto fail_assert_handler;
     }
 
-    event_notifier_set_handler(&cq->assert_notifier,
-                                nvme_assert_notifier_read);
+    if (with_irqfd) {
+        ret = nvme_kvm_msix_vector_use(n, cq, cq->vector);
+        if (ret < 0) {
+            goto fail_assert_handler;
+        }
+        ret = kvm_irqchip_add_irqfd_notifier_gsi(kvm_state,
+                                                 &cq->assert_notifier, NULL, 
+                                                 cq->virq);
+        if (ret < 0) {
+            goto fail_kvm;
+         }
+    } else {
+        event_notifier_set_handler(&cq->assert_notifier,
+                                   nvme_assert_notifier_read);
+    }
 
     if (!msix_enabled(&n->parent_obj)) {
         ret = event_notifier_init(&cq->deassert_notifier, 0);
@@ -1404,6 +1436,12 @@ static void nvme_init_irq_notifier(NvmeCtrl *n, 
NvmeCQueue *cq)
 fail_deassert_handler:
     event_notifier_set_handler(&cq->deassert_notifier, NULL);
     event_notifier_cleanup(&cq->deassert_notifier);
+    if (with_irqfd) {
+        kvm_irqchip_remove_irqfd_notifier_gsi(kvm_state, &cq->assert_notifier,
+                                              cq->virq);
+fail_kvm:
+        kvm_irqchip_release_virq(kvm_state, cq->virq);
+    }
 fail_assert_handler:
     event_notifier_set_handler(&cq->assert_notifier, NULL);
     event_notifier_cleanup(&cq->assert_notifier);
@@ -4783,6 +4821,8 @@ static uint16_t nvme_get_log(NvmeCtrl *n, NvmeRequest 
*req)
 
 static void nvme_free_cq(NvmeCQueue *cq, NvmeCtrl *n)
 {
+    bool with_irqfd = msix_enabled(&n->parent_obj) &&
+                      kvm_msi_via_irqfd_enabled();
     uint16_t offset = (cq->cqid << 3) + (1 << 2);
 
     n->cq[cq->cqid] = NULL;
@@ -4794,6 +4834,12 @@ static void nvme_free_cq(NvmeCQueue *cq, NvmeCtrl *n)
         event_notifier_cleanup(&cq->notifier);
     }
     if (cq->assert_notifier.initialized) {
+        if (with_irqfd) {
+            kvm_irqchip_remove_irqfd_notifier_gsi(kvm_state,
+                                                  &cq->assert_notifier, 
+                                                  cq->virq);
+            kvm_irqchip_release_virq(kvm_state, cq->virq);
+        }
         event_notifier_set_handler(&cq->assert_notifier, NULL);
         event_notifier_cleanup(&cq->assert_notifier);
     }
diff --git a/hw/nvme/nvme.h b/hw/nvme/nvme.h
index 759d0ecd7c..85fd9cd0e2 100644
--- a/hw/nvme/nvme.h
+++ b/hw/nvme/nvme.h
@@ -396,6 +396,7 @@ typedef struct NvmeCQueue {
     uint64_t    dma_addr;
     uint64_t    db_addr;
     uint64_t    ei_addr;
+    int         virq;
     QEMUTimer   *timer;
     EventNotifier notifier;
     EventNotifier assert_notifier;
-- 
2.25.1