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[79.178.12.128]) by smtp.gmail.com with ESMTPSA id t128sm4445039qke.4.2019.11.06.03.33.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Nov 2019 03:33:55 -0800 (PST) Date: Wed, 6 Nov 2019 06:33:51 -0500 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Subject: Re: [PATCH v2] virtio: notify virtqueue via host notifier when available Message-ID: <20191106063344-mutt-send-email-mst@kernel.org> References: <20191105140946.165584-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191105140946.165584-1-stefanha@redhat.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yongji Xie , qemu-devel@nongnu.org, felipe@nutanix.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Nov 05, 2019 at 03:09:46PM +0100, Stefan Hajnoczi wrote: > Host notifiers are used in several cases: > 1. Traditional ioeventfd where virtqueue notifications are handled in > the main loop thread. > 2. IOThreads (aio_handle_output) where virtqueue notifications are > handled in an IOThread AioContext. > 3. vhost where virtqueue notifications are handled by kernel vhost or > a vhost-user device backend. > > Most virtqueue notifications from the guest use the ioeventfd mechanism, > but there are corner cases where QEMU code calls virtio_queue_notify(). > This currently honors the host notifier for the IOThreads > aio_handle_output case, but not for the vhost case. The result is that > vhost does not receive virtqueue notifications from QEMU when > virtio_queue_notify() is called. > > This patch extends virtio_queue_notify() to set the host notifier > whenever it is enabled instead of calling the vq->(aio_)handle_output() > function directly. We track the host notifier state for each virtqueue > separately since some devices may use it only for certain virtqueues. > > This fixes the vhost case although it does add a trip through the > eventfd for the traditional ioeventfd case. I don't think it's worth > adding a fast path for the traditional ioeventfd case because calling > virtio_queue_notify() is rare when ioeventfd is enabled. > > Reported-by: Felipe Franciosi > Signed-off-by: Stefan Hajnoczi queued, thanks! > --- > v2: > * Track host notifier enabled/disabled state per virtqueue [Yongji Xie] > * Tested with contrib/vhost-user-blk and contrib/vhost-user-scsi > > hw/virtio/virtio-bus.c | 4 ++++ > hw/virtio/virtio.c | 9 ++++++++- > include/hw/virtio/virtio.h | 1 + > 3 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c > index b2c804292e..d6332d45c3 100644 > --- a/hw/virtio/virtio-bus.c > +++ b/hw/virtio/virtio-bus.c > @@ -288,6 +288,10 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign) > k->ioeventfd_assign(proxy, notifier, n, false); > } > > + if (r == 0) { > + virtio_queue_set_host_notifier_enabled(vq, assign); > + } > + > return r; > } > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 762df12f4c..04716b5f6c 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -128,6 +128,7 @@ struct VirtQueue > VirtIODevice *vdev; > EventNotifier guest_notifier; > EventNotifier host_notifier; > + bool host_notifier_enabled; > QLIST_ENTRY(VirtQueue) node; > }; > > @@ -2271,7 +2272,7 @@ void virtio_queue_notify(VirtIODevice *vdev, int n) > } > > trace_virtio_queue_notify(vdev, vq - vdev->vq, vq); > - if (vq->handle_aio_output) { > + if (vq->host_notifier_enabled) { > event_notifier_set(&vq->host_notifier); > } else if (vq->handle_output) { > vq->handle_output(vdev, vq); > @@ -3145,6 +3146,7 @@ void virtio_init(VirtIODevice *vdev, const char *name, > vdev->vq[i].vector = VIRTIO_NO_VECTOR; > vdev->vq[i].vdev = vdev; > vdev->vq[i].queue_index = i; > + vdev->vq[i].host_notifier_enabled = false; > } > > vdev->name = name; > @@ -3436,6 +3438,11 @@ EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq) > return &vq->host_notifier; > } > > +void virtio_queue_set_host_notifier_enabled(VirtQueue *vq, bool enabled) > +{ > + vq->host_notifier_enabled = enabled; > +} > + > int virtio_queue_set_host_notifier_mr(VirtIODevice *vdev, int n, > MemoryRegion *mr, bool assign) > { > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index 3448d67d2a..c32a815303 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -312,6 +312,7 @@ int virtio_device_grab_ioeventfd(VirtIODevice *vdev); > void virtio_device_release_ioeventfd(VirtIODevice *vdev); > bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev); > EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq); > +void virtio_queue_set_host_notifier_enabled(VirtQueue *vq, bool enabled); > void virtio_queue_host_notifier_read(EventNotifier *n); > void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx, > VirtIOHandleAIOOutput handle_output); > -- > 2.23.0