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Tsirkin" To: Stefano Garzarella Cc: Huaitong Han , marcel.apfelbaum@gmail.com, cohuck@redhat.com, pasic@linux.ibm.com, farman@linux.ibm.com, borntraeger@linux.ibm.com, leiyang@redhat.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org, Huaitong Han , Zhiyuan Yuan , Jidong Xia Subject: Re: [PATCH V2] vhost: Don't set vring call if guest notifier is unused Message-ID: <20250520080030-mutt-send-email-mst@kernel.org> References: <20250513112825.1731347-1-hanht2@chinatelecom.cn> <5cstdapha4xzmgkuja5ydxxvfgr4ux5iytex3qp65vm5hedp7s@h2mjfv72npyw> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.487, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, May 20, 2025 at 01:04:10PM +0200, Stefano Garzarella wrote: > On Fri, May 16, 2025 at 09:03:33PM +0800, Huaitong Han wrote: > > Stefano Garzarella 于2025年5月16日周五 16:19写道： > > > > > > On Tue, May 13, 2025 at 07:28:25PM +0800, oenhan@gmail.com wrote: > > > >From: Huaitong Han > > > > > > > >The vring call fd is set even when the guest does not use MSI-X (e.g., in the > > > >case of virtio PMD), leading to unnecessary CPU overhead for processing > > > >interrupts. > > > > > > > >The commit 96a3d98d2c("vhost: don't set vring call if no vector") optimized the > > > >case where MSI-X is enabled but the queue vector is unset. However, there's an > > > >additional case where the guest uses INTx and the INTx_DISABLED bit in the PCI > > > >config is set, meaning that no interrupt notifier will actually be used. > > > > > > > >In such cases, the vring call fd should also be cleared to avoid redundant > > > >interrupt handling. > > > > > > > >Fixes: 96a3d98d2c("vhost: don't set vring call if no vector") > > > >Reported-by: Zhiyuan Yuan > > > >Signed-off-by: Jidong Xia > > > >Signed-off-by: Huaitong Han > > > >--- > > > >V2: > > > >- Retain the name `query_guest_notifiers` > > > >- All qtest/unit test cases pass > > > >- Fix V1 patch style problems > > > > > > > > hw/pci/pci.c | 2 +- > > > > hw/s390x/virtio-ccw.c | 7 +++++-- > > > > hw/virtio/vhost.c | 3 +-- > > > > hw/virtio/virtio-pci.c | 10 ++++++++-- > > > > include/hw/pci/pci.h | 1 + > > > > include/hw/virtio/virtio-bus.h | 2 +- > > > > 6 files changed, 17 insertions(+), 8 deletions(-) > > > > > > > >diff --git a/hw/pci/pci.c b/hw/pci/pci.c > > > >index 352b3d12c8..45b491412a 100644 > > > >--- a/hw/pci/pci.c > > > >+++ b/hw/pci/pci.c > > > >@@ -1712,7 +1712,7 @@ 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) > > > > > > Since it was inline, will it be better to move the whole function to > > > include/hw/pci/pci.h and keep it inline? > > > > > I did try moving the function to include/hw/pci/pci.h and marking it > > inline, but ran into compilation issues due to the use of the incomplete > > PCIDevice type. > > Specifically, accessing d->config triggers the following error: > > include/hw/pci/pci.h:674:26: error: invalid use of incomplete typedef > > ‘PCIDevice’ > > return pci_get_word(d->config + PCI_COMMAND) & PCI_COMMAND_INTX_DISABLE; > > Including hw/pci/pci_device.h in pci.h to resolve this introduces > > further issues, so I suggest to keep the function as a non-inline > > helper in the .c file. > > I see. If Michael is happy with that, it's fine by me! > > Thanks, > Stefano > I think it's fine. > > > Thanks, > > > Stefano > > > > > > > { > > > > 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 d2f85b39f3..632708ba4d 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(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) > > > >diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > > > >index 4cae7c1664..2a9a839763 100644 > > > >--- a/hw/virtio/vhost.c > > > >+++ b/hw/virtio/vhost.c > > > >@@ -1341,8 +1341,7 @@ int vhost_virtqueue_start(struct vhost_dev *dev, > > > > } > > > > > > > > if (k->query_guest_notifiers && > > > >- k->query_guest_notifiers(qbus->parent) && > > > >- virtio_queue_vector(vdev, idx) == VIRTIO_NO_VECTOR) { > > > >+ !k->query_guest_notifiers(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 0fa8fe4955..d62e199489 100644 > > > >--- a/hw/virtio/virtio-pci.c > > > >+++ b/hw/virtio/virtio-pci.c > > > >@@ -1212,10 +1212,16 @@ 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(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) > > > >diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h > > > >index c2fe6caa2c..8c24bd97db 100644 > > > >--- a/include/hw/pci/pci.h > > > >+++ b/include/hw/pci/pci.h > > > >@@ -668,6 +668,7 @@ void lsi53c8xx_handle_legacy_cmdline(DeviceState *lsi_dev); > > > > > > > > qemu_irq pci_allocate_irq(PCIDevice *pci_dev); > > > > void pci_set_irq(PCIDevice *pci_dev, int level); > > > >+int pci_irq_disabled(PCIDevice *d); > > > > > > > > static inline void pci_irq_assert(PCIDevice *pci_dev) > > > > { > > > >diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h > > > >index 7ab8c9dab0..75d43b508a 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)(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 > > > > > > > > >