diff mbox series

vhost: Don't set vring call if guest notifier is unused

Message ID 20250326082537.379977-1-hanht2@chinatelecom.cn (mailing list archive)
State New
Headers show
Series vhost: Don't set vring call if guest notifier is unused | expand

Commit Message

oenhan@gmail.com March 26, 2025, 8:25 a.m. UTC 
From: Huaitong Han <hanht2@chinatelecom.cn>

The vring call fd is set even when the guest does not use msix (e.g., in the
case of virtio pmd), leading to unnecessary CPU overhead for processing
interrupts. The previous patch optimized the condition where msix is enabled
but the queue vector is unset. However, there is a additional case where the
guest interrupt notifier is effectively unused and the vring call fd should
also be cleared: the guest does not use msix and the INTX_DISABLED bit in the PCI
config is set.

Fixes: 96a3d98d2c ("vhost: don't set vring call if no vector")

Test result:
https://raw.githubusercontent.com/oenhan/build_log/refs/heads/main/qemu/2503261015/build/meson-logs/testlog.txt

Reported-by: Zhiyuan Yuan <yuanzhiyuan@chinatelecom.cn>
Signed-off-by: Jidong Xia <xiajd@chinatelecom.cn>
Signed-off-by: Huaitong Han <hanht2@chinatelecom.cn>
---
 hw/pci/pci.c                   |  2 +-
 hw/s390x/virtio-ccw.c          |  9 ++++++---
 hw/virtio/vhost.c              |  5 ++---
 hw/virtio/virtio-pci.c         | 15 ++++++++++-----
 include/hw/pci/pci.h           |  1 +
 include/hw/virtio/virtio-bus.h |  2 +-
 6 files changed, 21 insertions(+), 13 deletions(-)

Comments

Stefano Garzarella April 1, 2025, 10:49 a.m. UTC | #1 
On Wed, Mar 26, 2025 at 04:25:37PM +0800, oenhan@gmail.com wrote:
>From: Huaitong Han <hanht2@chinatelecom.cn>
>
>The vring call fd is set even when the guest does not use msix (e.g., in the
>case of virtio pmd), leading to unnecessary CPU overhead for processing
>interrupts. The previous patch optimized the condition where msix is 

What would be the previous patch?

If you're referencing a patch already merged, please add them in the 
same form you used in Fixes, for example:
Commit XXXXX ("vhost: ...") optimized the condition ...

>enabled
>but the queue vector is unset. However, there is a additional case where the
>guest interrupt notifier is effectively unused and the vring call fd should
>also be cleared: the guest does not use msix and the INTX_DISABLED bit in the PCI
>config is set.

I don't know this code very well, can you explain better what you are 
changing with this patch and why change the name of 
query_guest_notifiers?

>
>Fixes: 96a3d98d2c ("vhost: don't set vring call if no vector")
>
>Test result:
>https://raw.githubusercontent.com/oenhan/build_log/refs/heads/main/qemu/2503261015/build/meson-logs/testlog.txt

Does it make sense to have this link in the commit, will it always be 
accessible?

>
>Reported-by: Zhiyuan Yuan <yuanzhiyuan@chinatelecom.cn>
>Signed-off-by: Jidong Xia <xiajd@chinatelecom.cn>
>Signed-off-by: Huaitong Han <hanht2@chinatelecom.cn>
>---
> hw/pci/pci.c                   |  2 +-
> hw/s390x/virtio-ccw.c          |  9 ++++++---
> hw/virtio/vhost.c              |  5 ++---
> hw/virtio/virtio-pci.c         | 15 ++++++++++-----
> include/hw/pci/pci.h           |  1 +
> include/hw/virtio/virtio-bus.h |  2 +-
> 6 files changed, 21 insertions(+), 13 deletions(-)
>
>diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>index 2844ec5556..503a897528 100644
>--- a/hw/pci/pci.c
>+++ b/hw/pci/pci.c
>@@ -1719,7 +1719,7 @@ static void pci_update_mappings(PCIDevice *d)
>     pci_update_vga(d);
> }
>
>-static inline int pci_irq_disabled(PCIDevice *d)
>+int pci_irq_disabled(PCIDevice *d)
> {
>     return pci_get_word(d->config + PCI_COMMAND) & PCI_COMMAND_INTX_DISABLE;
> }
>diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
>index 43f3b162c8..af482a22cd 100644
>--- a/hw/s390x/virtio-ccw.c
>+++ b/hw/s390x/virtio-ccw.c
>@@ -936,11 +936,14 @@ static void virtio_ccw_vmstate_change(DeviceState *d, bool running)
>     }
> }
>
>-static bool virtio_ccw_query_guest_notifiers(DeviceState *d)
>+static bool virtio_ccw_query_guest_notifiers_used(DeviceState *d, int n)
> {
>     CcwDevice *dev = CCW_DEVICE(d);
>+    VirtioCcwDevice *vdev = VIRTIO_CCW_DEVICE(d);
>+    VirtIODevice *virtio_dev = virtio_bus_get_device(&vdev->bus);
>
>-    return !!(dev->sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA);
>+    return !!(dev->sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA)
>+            && virtio_queue_vector(virtio_dev, n) != VIRTIO_NO_VECTOR;
> }
>
> static int virtio_ccw_get_mappings(VirtioCcwDevice *dev)
>@@ -1270,7 +1273,7 @@ static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
>     bus_class->max_dev = 1;
>     k->notify = virtio_ccw_notify;
>     k->vmstate_change = virtio_ccw_vmstate_change;
>-    k->query_guest_notifiers = virtio_ccw_query_guest_notifiers;
>+    k->query_guest_notifiers_used = virtio_ccw_query_guest_notifiers_used;
>     k->set_guest_notifiers = virtio_ccw_set_guest_notifiers;
>     k->save_queue = virtio_ccw_save_queue;
>     k->load_queue = virtio_ccw_load_queue;
>diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>index 6aa72fd434..32634da836 100644
>--- a/hw/virtio/vhost.c
>+++ b/hw/virtio/vhost.c
>@@ -1341,9 +1341,8 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
>         vhost_virtqueue_mask(dev, vdev, idx, false);
>     }
>
>-    if (k->query_guest_notifiers &&
>-        k->query_guest_notifiers(qbus->parent) &&
>-        virtio_queue_vector(vdev, idx) == VIRTIO_NO_VECTOR) {
>+    if (k->query_guest_notifiers_used &&
>+        !k->query_guest_notifiers_used(qbus->parent, idx)) {
>         file.fd = -1;
>         r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
>         if (r) {
>diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>index 3ca3f849d3..25ff869618 100644
>--- a/hw/virtio/virtio-pci.c
>+++ b/hw/virtio/virtio-pci.c
>@@ -30,6 +30,7 @@
> #include "qemu/error-report.h"
> #include "qemu/log.h"
> #include "qemu/module.h"
>+#include "hw/pci/pci.h"
> #include "hw/pci/msi.h"
> #include "hw/pci/msix.h"
> #include "hw/loader.h"
>@@ -1031,7 +1032,7 @@ static void virtio_pci_one_vector_mask(VirtIOPCIProxy *proxy,
>
>     /* If guest supports masking, keep irqfd but mask it.
>      * Otherwise, clean it up now.
>-     */
>+     */

Unrelated change.

>     if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>         k->guest_notifier_mask(vdev, queue_no, true);
>     } else {
>@@ -1212,10 +1213,15 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
>     return 0;
> }
>
>-static bool virtio_pci_query_guest_notifiers(DeviceState *d)
>+static bool virtio_pci_query_guest_notifiers_used(DeviceState *d, int n)
> {
>     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
>-    return msix_enabled(&proxy->pci_dev);
>+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
>+
>+    if (msix_enabled(&proxy->pci_dev))
>+        return virtio_queue_vector(vdev, n) != VIRTIO_NO_VECTOR;
>+    else
>+        return !pci_irq_disabled(&proxy->pci_dev);
> }
>
> static int virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool assign)
>@@ -2599,7 +2605,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
>     k->save_extra_state = virtio_pci_save_extra_state;
>     k->load_extra_state = virtio_pci_load_extra_state;
>     k->has_extra_state = virtio_pci_has_extra_state;
>-    k->query_guest_notifiers = virtio_pci_query_guest_notifiers;
>+    k->query_guest_notifiers_used = virtio_pci_query_guest_notifiers_used;
>     k->set_guest_notifiers = virtio_pci_set_guest_notifiers;
>     k->set_host_notifier_mr = virtio_pci_set_host_notifier_mr;
>     k->vmstate_change = virtio_pci_vmstate_change;
>@@ -2630,4 +2636,3 @@ static void virtio_pci_register_types(void)
> }
>
> type_init(virtio_pci_register_types)
>-
>diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>index 822fbacdf0..de4ab28046 100644
>--- a/include/hw/pci/pci.h
>+++ b/include/hw/pci/pci.h
>@@ -256,6 +256,7 @@ void pci_del_capability(PCIDevice *pci_dev, uint8_t cap_id, uint8_t cap_size);
>
> uint8_t pci_find_capability(PCIDevice *pci_dev, uint8_t cap_id);
>
>+int pci_irq_disabled(PCIDevice *d);
>
> uint32_t pci_default_read_config(PCIDevice *d,
>                                  uint32_t address, int len);
>diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
>index 7ab8c9dab0..de75a44895 100644
>--- a/include/hw/virtio/virtio-bus.h
>+++ b/include/hw/virtio/virtio-bus.h
>@@ -48,7 +48,7 @@ struct VirtioBusClass {
>     int (*load_done)(DeviceState *d, QEMUFile *f);
>     int (*load_extra_state)(DeviceState *d, QEMUFile *f);
>     bool (*has_extra_state)(DeviceState *d);
>-    bool (*query_guest_notifiers)(DeviceState *d);
>+    bool (*query_guest_notifiers_used)(DeviceState *d, int n);
>     int (*set_guest_notifiers)(DeviceState *d, int nvqs, bool assign);
>     int (*set_host_notifier_mr)(DeviceState *d, int n,
>                                 MemoryRegion *mr, bool assign);
>-- 
>2.43.5
>
diff mbox series

Patch

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 2844ec5556..503a897528 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -1719,7 +1719,7 @@  static void pci_update_mappings(PCIDevice *d)
     pci_update_vga(d);
 }
 
-static inline int pci_irq_disabled(PCIDevice *d)
+int pci_irq_disabled(PCIDevice *d)
 {
     return pci_get_word(d->config + PCI_COMMAND) & PCI_COMMAND_INTX_DISABLE;
 }
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 43f3b162c8..af482a22cd 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -936,11 +936,14 @@  static void virtio_ccw_vmstate_change(DeviceState *d, bool running)
     }
 }
 
-static bool virtio_ccw_query_guest_notifiers(DeviceState *d)
+static bool virtio_ccw_query_guest_notifiers_used(DeviceState *d, int n)
 {
     CcwDevice *dev = CCW_DEVICE(d);
+    VirtioCcwDevice *vdev = VIRTIO_CCW_DEVICE(d);
+    VirtIODevice *virtio_dev = virtio_bus_get_device(&vdev->bus);
 
-    return !!(dev->sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA);
+    return !!(dev->sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA)
+            && virtio_queue_vector(virtio_dev, n) != VIRTIO_NO_VECTOR;
 }
 
 static int virtio_ccw_get_mappings(VirtioCcwDevice *dev)
@@ -1270,7 +1273,7 @@  static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
     bus_class->max_dev = 1;
     k->notify = virtio_ccw_notify;
     k->vmstate_change = virtio_ccw_vmstate_change;
-    k->query_guest_notifiers = virtio_ccw_query_guest_notifiers;
+    k->query_guest_notifiers_used = virtio_ccw_query_guest_notifiers_used;
     k->set_guest_notifiers = virtio_ccw_set_guest_notifiers;
     k->save_queue = virtio_ccw_save_queue;
     k->load_queue = virtio_ccw_load_queue;
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 6aa72fd434..32634da836 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1341,9 +1341,8 @@  int vhost_virtqueue_start(struct vhost_dev *dev,
         vhost_virtqueue_mask(dev, vdev, idx, false);
     }
 
-    if (k->query_guest_notifiers &&
-        k->query_guest_notifiers(qbus->parent) &&
-        virtio_queue_vector(vdev, idx) == VIRTIO_NO_VECTOR) {
+    if (k->query_guest_notifiers_used &&
+        !k->query_guest_notifiers_used(qbus->parent, idx)) {
         file.fd = -1;
         r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
         if (r) {
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 3ca3f849d3..25ff869618 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -30,6 +30,7 @@ 
 #include "qemu/error-report.h"
 #include "qemu/log.h"
 #include "qemu/module.h"
+#include "hw/pci/pci.h"
 #include "hw/pci/msi.h"
 #include "hw/pci/msix.h"
 #include "hw/loader.h"
@@ -1031,7 +1032,7 @@  static void virtio_pci_one_vector_mask(VirtIOPCIProxy *proxy,
 
     /* If guest supports masking, keep irqfd but mask it.
      * Otherwise, clean it up now.
-     */ 
+     */
     if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
         k->guest_notifier_mask(vdev, queue_no, true);
     } else {
@@ -1212,10 +1213,15 @@  static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
     return 0;
 }
 
-static bool virtio_pci_query_guest_notifiers(DeviceState *d)
+static bool virtio_pci_query_guest_notifiers_used(DeviceState *d, int n)
 {
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
-    return msix_enabled(&proxy->pci_dev);
+    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
+
+    if (msix_enabled(&proxy->pci_dev))
+        return virtio_queue_vector(vdev, n) != VIRTIO_NO_VECTOR;
+    else
+        return !pci_irq_disabled(&proxy->pci_dev);
 }
 
 static int virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool assign)
@@ -2599,7 +2605,7 @@  static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
     k->save_extra_state = virtio_pci_save_extra_state;
     k->load_extra_state = virtio_pci_load_extra_state;
     k->has_extra_state = virtio_pci_has_extra_state;
-    k->query_guest_notifiers = virtio_pci_query_guest_notifiers;
+    k->query_guest_notifiers_used = virtio_pci_query_guest_notifiers_used;
     k->set_guest_notifiers = virtio_pci_set_guest_notifiers;
     k->set_host_notifier_mr = virtio_pci_set_host_notifier_mr;
     k->vmstate_change = virtio_pci_vmstate_change;
@@ -2630,4 +2636,3 @@  static void virtio_pci_register_types(void)
 }
 
 type_init(virtio_pci_register_types)
-
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index 822fbacdf0..de4ab28046 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -256,6 +256,7 @@  void pci_del_capability(PCIDevice *pci_dev, uint8_t cap_id, uint8_t cap_size);
 
 uint8_t pci_find_capability(PCIDevice *pci_dev, uint8_t cap_id);
 
+int pci_irq_disabled(PCIDevice *d);
 
 uint32_t pci_default_read_config(PCIDevice *d,
                                  uint32_t address, int len);
diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index 7ab8c9dab0..de75a44895 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -48,7 +48,7 @@  struct VirtioBusClass {
     int (*load_done)(DeviceState *d, QEMUFile *f);
     int (*load_extra_state)(DeviceState *d, QEMUFile *f);
     bool (*has_extra_state)(DeviceState *d);
-    bool (*query_guest_notifiers)(DeviceState *d);
+    bool (*query_guest_notifiers_used)(DeviceState *d, int n);
     int (*set_guest_notifiers)(DeviceState *d, int nvqs, bool assign);
     int (*set_host_notifier_mr)(DeviceState *d, int n,
                                 MemoryRegion *mr, bool assign);