[Qemu-devel] [PATCH 0/4] ioeventfd support for virtio-mmio

[Qemu-devel] [PATCH 0/4] ioeventfd support for virtio-mmio

[Ying-Shiuan Pan]

I added host/guest notifiers support for virtio-mmio, so that qemu can
enable vhost-net for kvm-arm. Sorry for that I cannot measure the performance
difference because I have only Exynos-5250 arndale boards which only provide
a 100 Mbps Ethernet. But in our previous work in kvm-arm (refer: Evaluation of
a Server-Grade Software-Only ARM Hypervisor), the vhost-net increased at least
30% in throughput comparing to virtio-net.

Ying-Shiuan Pan (4):
  virtio-mmio: introduce set_host_notifier()
  virtio-mmio: introduce set_guest_notifiers
  virtio-mmio: start ioeventfd when status gets DRIVER_OK
  virtio-mmio: add a new property for ioeventfd

 hw/block/virtio-blk.c      |   1 +
 hw/net/virtio-net.c        |   1 +
 hw/virtio/virtio-mmio.c    | 176 +++++++++++++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio.h |   1 +
 4 files changed, 179 insertions(+)

-- 
1.8.1.2

[Qemu-devel] [PATCH 1/4] virtio-mmio: introduce set_host_notifier()

[Ying-Shiuan Pan]

set_host_notifier() is introduced into virtio-mmio now. Most of codes came
from virtio-pci.

Signed-off-by: Ying-Shiuan Pan <yspan@itri.org.tw>
---
 hw/virtio/virtio-mmio.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index 8829eb0..558fd2f 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -23,6 +23,7 @@
 #include "hw/virtio/virtio.h"
 #include "qemu/host-utils.h"
 #include "hw/virtio/virtio-bus.h"
+#include "qemu/error-report.h"
 
 /* #define DEBUG_VIRTIO_MMIO */
 
@@ -87,11 +88,61 @@ typedef struct {
     uint32_t guest_page_shift;
     /* virtio-bus */
     VirtioBusState bus;
+    bool ioeventfd_disabled;
+    bool ioeventfd_started;
 } VirtIOMMIOProxy;
 
 static void virtio_mmio_bus_new(VirtioBusState *bus, size_t bus_size,
                                 VirtIOMMIOProxy *dev);
 
+static int virtio_mmio_set_host_notifier_internal(VirtIOMMIOProxy *proxy,
+                                                 int n, bool assign, bool set_handler)
+{
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+    VirtQueue *vq = virtio_get_queue(vdev, n);
+    EventNotifier *notifier = virtio_queue_get_host_notifier(vq);
+    int r = 0;
+
+    if (assign) {
+        r = event_notifier_init(notifier, 1);
+        if (r < 0) {
+            error_report("%s: unable to init event notifier: %d",
+                         __func__, r);
+            return r;
+        }
+        virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
+        memory_region_add_eventfd(&proxy->iomem, VIRTIO_MMIO_QUEUENOTIFY, 4,
+                                  true, n, notifier);
+    } else {
+        memory_region_del_eventfd(&proxy->iomem, VIRTIO_MMIO_QUEUENOTIFY, 4,
+                                  true, n, notifier);
+        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
+        event_notifier_cleanup(notifier);
+    }
+    return r;
+}
+
+static void virtio_mmio_stop_ioeventfd(VirtIOMMIOProxy *proxy)
+{
+    int r;
+    int n;
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+
+    if (!proxy->ioeventfd_started) {
+        return;
+    }
+
+    for (n = 0; n < VIRTIO_PCI_QUEUE_MAX; n++) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+
+        r = virtio_mmio_set_host_notifier_internal(proxy, n, false, false);
+        assert(r >= 0);
+    }
+    proxy->ioeventfd_started = false;
+}
+
 static uint64_t virtio_mmio_read(void *opaque, hwaddr offset, unsigned size)
 {
     VirtIOMMIOProxy *proxy = (VirtIOMMIOProxy *)opaque;
@@ -345,6 +396,24 @@ static void virtio_mmio_reset(DeviceState *d)
     proxy->guest_page_shift = 0;
 }
 
+static int virtio_mmio_set_host_notifier(DeviceState *opaque, int n, bool assign)
+{
+    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
+
+    /* Stop using ioeventfd for virtqueue kick if the device starts using host
+     * notifiers.  This makes it easy to avoid stepping on each others' toes.
+     */
+    proxy->ioeventfd_disabled = assign;
+    if (assign) {
+        virtio_mmio_stop_ioeventfd(proxy);
+    }
+    /* We don't need to start here: it's not needed because backend
+     * currently only stops on status change away from ok,
+     * reset, vmstop and such. If we do add code to start here,
+     * need to check vmstate, device state etc. */
+    return virtio_mmio_set_host_notifier_internal(proxy, n, assign, false);
+}
+
 /* virtio-mmio device */
 
 /* This is called by virtio-bus just after the device is plugged. */
@@ -406,6 +475,7 @@ static void virtio_mmio_bus_class_init(ObjectClass *klass, void *data)
     k->notify = virtio_mmio_update_irq;
     k->save_config = virtio_mmio_save_config;
     k->load_config = virtio_mmio_load_config;
+    k->set_host_notifier = virtio_mmio_set_host_notifier;
     k->get_features = virtio_mmio_get_features;
     k->device_plugged = virtio_mmio_device_plugged;
     k->has_variable_vring_alignment = true;
-- 
1.8.1.2

[Qemu-devel] [PATCH 2/4] virtio-mmio: introduce set_guest_notifiers

[Ying-Shiuan Pan]

Same as host notifier of virtio-mmio, most of codes came from virtio-pci.
The kvm-arm does not yet support irqfd, need to fix the hard-coded part after
kvm-arm gets irqfd support.

Signed-off-by: Ying-Shiuan Pan <yspan@itri.org.tw>
---
 hw/virtio/virtio-mmio.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index 558fd2f..f95b7dd 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -396,6 +396,65 @@ static void virtio_mmio_reset(DeviceState *d)
     proxy->guest_page_shift = 0;
 }
 
+static int virtio_mmio_set_guest_notifier(DeviceState *d, int n, bool assign,
+                                         bool with_irqfd)
+{
+    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(d);
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
+    VirtQueue *vq = virtio_get_queue(vdev, n);
+    EventNotifier *notifier = virtio_queue_get_guest_notifier(vq);
+
+    if (assign) {
+        int r = event_notifier_init(notifier, 0);
+        if (r < 0) {
+            return r;
+        }
+        virtio_queue_set_guest_notifier_fd_handler(vq, true, with_irqfd);
+    } else {
+        virtio_queue_set_guest_notifier_fd_handler(vq, false, with_irqfd);
+        event_notifier_cleanup(notifier);
+    }
+
+    if (vdc->guest_notifier_mask) {
+        vdc->guest_notifier_mask(vdev, n, !assign);
+    }
+
+    return 0;
+}
+
+static int virtio_mmio_set_guest_notifiers(DeviceState *d, int nvqs, bool assign)
+{
+    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(d);
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+    /* TODO: need to check if kvm-arm supports irqfd */
+    bool with_irqfd = false;
+    int r, n;
+
+    nvqs = MIN(nvqs, VIRTIO_PCI_QUEUE_MAX);
+
+    for (n = 0; n < nvqs; n++) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            break;
+        }
+
+        r = virtio_mmio_set_guest_notifier(d, n, assign, with_irqfd);
+        if (r < 0) {
+            goto assign_error;
+        }
+    }
+
+    return 0;
+
+assign_error:
+    /* We get here on assignment failure. Recover by undoing for VQs 0 .. n. */
+    assert(assign);
+    while (--n >= 0) {
+        virtio_mmio_set_guest_notifier(d, n, !assign, false);
+    }
+    return r;
+}
+
 static int virtio_mmio_set_host_notifier(DeviceState *opaque, int n, bool assign)
 {
     VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
@@ -476,6 +535,7 @@ static void virtio_mmio_bus_class_init(ObjectClass *klass, void *data)
     k->save_config = virtio_mmio_save_config;
     k->load_config = virtio_mmio_load_config;
     k->set_host_notifier = virtio_mmio_set_host_notifier;
+    k->set_guest_notifiers = virtio_mmio_set_guest_notifiers;
     k->get_features = virtio_mmio_get_features;
     k->device_plugged = virtio_mmio_device_plugged;
     k->has_variable_vring_alignment = true;
-- 
1.8.1.2

[Qemu-devel] [PATCH 3/4] virtio-mmio: start ioeventfd when status gets DRIVER_OK

[Ying-Shiuan Pan]

Signed-off-by: Ying-Shiuan Pan <yspan@itri.org.tw>
---
 hw/virtio/virtio-mmio.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index f95b7dd..11964ee 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -122,6 +122,42 @@ static int virtio_mmio_set_host_notifier_internal(VirtIOMMIOProxy *proxy,
     return r;
 }
 
+static void virtio_mmio_start_ioeventfd(VirtIOMMIOProxy *proxy)
+{
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+    int n, r;
+
+    if (proxy->ioeventfd_disabled ||
+        proxy->ioeventfd_started) {
+        return;
+    }
+
+    for (n = 0; n < VIRTIO_PCI_QUEUE_MAX; n++) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+
+        r = virtio_mmio_set_host_notifier_internal(proxy, n, true, true);
+        if (r < 0) {
+            goto assign_error;
+        }
+    }
+    proxy->ioeventfd_started = true;
+    return;
+
+assign_error:
+    while (--n >= 0) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+
+        r = virtio_mmio_set_host_notifier_internal(proxy, n, false, false);
+        assert(r >= 0);
+    }
+    proxy->ioeventfd_started = false;
+    error_report("%s: failed. Fallback to a userspace (slower).", __func__);
+}
+
 static void virtio_mmio_stop_ioeventfd(VirtIOMMIOProxy *proxy)
 {
     int r;
@@ -320,7 +356,16 @@ static void virtio_mmio_write(void *opaque, hwaddr offset, uint64_t value,
         virtio_update_irq(vdev);
         break;
     case VIRTIO_MMIO_STATUS:
+        if (!(value & VIRTIO_CONFIG_S_DRIVER_OK)) {
+            virtio_mmio_stop_ioeventfd(proxy);
+        }
+
         virtio_set_status(vdev, value & 0xff);
+
+        if (value & VIRTIO_CONFIG_S_DRIVER_OK) {
+            virtio_mmio_start_ioeventfd(proxy);
+        }
+
         if (vdev->status == 0) {
             virtio_reset(vdev);
         }
-- 
1.8.1.2

[Qemu-devel] [PATCH 4/4] virtio-mmio: add a new property for ioeventfd

[Ying-Shiuan Pan]

Make ioeventfd could be enabled or disabled (default). Since ioeventfd
is not yet ready in kvm-arm, without this option, qemu will get a
problem if it attempts to initialize ioeventfd.

To coincide this option of virtio-mmio with virtio-pci, I would like to
also move VIRTIO_PCI_FLAG_USE_IOEVENTFD to 'bool ioeventfd' of VirtIODevice.
Any better suggestion?

Signed-off-by: Ying-Shiuan Pan <yspan@itri.org.tw>
---
 hw/block/virtio-blk.c      | 1 +
 hw/net/virtio-net.c        | 1 +
 hw/virtio/virtio-mmio.c    | 3 ++-
 include/hw/virtio/virtio.h | 1 +
 4 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 19d0961..befdfdf 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -756,6 +756,7 @@ static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
 
 static Property virtio_blk_properties[] = {
     DEFINE_VIRTIO_BLK_PROPERTIES(VirtIOBlock, blk),
+    DEFINE_PROP_BOOL("ioeventfd", VirtIOBlock, parent_obj.use_ioeventfd, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 3626608..9b75e61 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1631,6 +1631,7 @@ static Property virtio_net_properties[] = {
                                                TX_TIMER_INTERVAL),
     DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
     DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
+    DEFINE_PROP_BOOL("ioeventfd", VirtIONet, parent_obj.use_ioeventfd, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index 11964ee..3f7a341 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -127,7 +127,8 @@ static void virtio_mmio_start_ioeventfd(VirtIOMMIOProxy *proxy)
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
     int n, r;
 
-    if (proxy->ioeventfd_disabled ||
+    if (!vdev->use_ioeventfd ||
+        proxy->ioeventfd_disabled ||
         proxy->ioeventfd_started) {
         return;
     }
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 3e54e90..d4cb3bf 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -121,6 +121,7 @@ struct VirtIODevice
     bool vm_running;
     VMChangeStateEntry *vmstate;
     char *bus_name;
+    bool use_ioeventfd;
 };
 
 typedef struct VirtioDeviceClass {
-- 
1.8.1.2

[Qemu-devel] [PATCH 4/4] virtio-mmio: add a new property for ioeventfd

[Shannon Zhao]

Make ioeventfd could be enabled or disabled (default). Since ioeventfd
is not yet ready in kvm-arm, without this option, qemu will get a
problem if it attempts to initialize ioeventfd.

Signed-off-by: Ying-Shiuan Pan <yingshiuan.pan@gmail.com>
Signed-off-by: Li Liu <john.liuli@huawei.com>
Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>
---
 hw/net/virtio-net.c        |    1 +
 hw/virtio/virtio-mmio.c    |    3 ++-
 include/hw/virtio/virtio.h |    1 +
 3 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 9b88775..d89d4a6 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1723,6 +1723,7 @@ static Property virtio_net_properties[] = {
                                                TX_TIMER_INTERVAL),
     DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
     DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
+    DEFINE_PROP_BOOL("ioeventfd", VirtIONet, parent_obj.use_ioeventfd, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index c543e71..16697ed 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -124,7 +124,8 @@ static void virtio_mmio_start_ioeventfd(VirtIOMMIOProxy *proxy)
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
     int n, r;
 
-    if (proxy->ioeventfd_disabled ||
+    if (!vdev->use_ioeventfd ||
+        proxy->ioeventfd_disabled ||
         proxy->ioeventfd_started) {
         return;
     }
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 0726d76..e4bc8ad 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -127,6 +127,7 @@ struct VirtIODevice
     bool vm_running;
     VMChangeStateEntry *vmstate;
     char *bus_name;
+    bool use_ioeventfd;
     uint8_t device_endian;
 };
 
-- 
1.7.1