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Tsirkin" To: "Longpeng(Mike)" Cc: jasowang@redhat.com, pbonzini@redhat.com, arei.gonglei@huawei.com, yechuan@huawei.com, eperezma@redhat.com, alex.williamson@redhat.com, mtosatti@redhat.com, clg@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH v1 1/3] virtio-pci: submit msi route changes in batch Message-ID: <20230228051619-mutt-send-email-mst@kernel.org> References: <20230228093937.2515-1-longpeng2@huawei.com> <20230228093937.2515-2-longpeng2@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230228093937.2515-2-longpeng2@huawei.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-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, Feb 28, 2023 at 05:39:35PM +0800, Longpeng(Mike) wrote: > From: Longpeng > > The kvm_irqchip_commit_routes() is a time-intensive operation, it needs > scan and update all irqfds that are already assigned during each invocation, > so more vectors means need more time to process them. I think the real reason is it's the write side of RCU. > For virtio-pci, we > can just submit once when enabling vectors of a virtio-pci device. > > This can reduce the downtime when migrating a VM with vhost-vdpa devices. > > Signed-off-by: Longpeng > --- > hw/virtio/virtio-pci.c | 24 +++++++++++++++++++++--- > 1 file changed, 21 insertions(+), 3 deletions(-) > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 247325c193..22e76e3902 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -49,6 +49,19 @@ > * configuration space */ > #define VIRTIO_PCI_CONFIG_SIZE(dev) VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev)) > > +/* Protected by the BQL */ > +static KVMRouteChange virtio_pci_route_change; > + > +static inline void virtio_pci_begin_route_changes(void) > +{ > + virtio_pci_route_change = kvm_irqchip_begin_route_changes(kvm_state); > +} > + > +static inline void virtio_pci_commit_route_changes(void) > +{ > + kvm_irqchip_commit_route_changes(&virtio_pci_route_change); > +} > + > static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size, > VirtIOPCIProxy *dev); > static void virtio_pci_reset(DeviceState *qdev); > @@ -790,12 +803,11 @@ static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy, > int ret; > > if (irqfd->users == 0) { > - KVMRouteChange c = kvm_irqchip_begin_route_changes(kvm_state); > - ret = kvm_irqchip_add_msi_route(&c, vector, &proxy->pci_dev); > + ret = kvm_irqchip_add_msi_route(&virtio_pci_route_change, vector, > + &proxy->pci_dev); > if (ret < 0) { > return ret; > } > - kvm_irqchip_commit_route_changes(&c); > irqfd->virq = ret; > } > irqfd->users++; > @@ -903,12 +915,18 @@ static int kvm_virtio_pci_vector_vq_use(VirtIOPCIProxy *proxy, int nvqs) > int ret = 0; > VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus); > > + virtio_pci_begin_route_changes(); > + > for (queue_no = 0; queue_no < nvqs; queue_no++) { > if (!virtio_queue_get_num(vdev, queue_no)) { > + virtio_pci_commit_route_changes(); > return -1; > } > ret = kvm_virtio_pci_vector_use_one(proxy, queue_no); > } > + > + virtio_pci_commit_route_changes(); > + > return ret; > } > > -- > 2.23.0