Re: Re: [RFC v7] virtio/vsock: add two more queues for datagram types

[Jiang Wang .]

On Wed, Sep 22, 2021 at 2:23 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> On Wed, Sep 22, 2021 at 12:00:24AM +0000, Jiang Wang wrote:
> >Datagram sockets are connectionless and unreliable.
> >The sender does not know the capacity of the receiver
> >and may send more packets than the receiver can handle.
> >
> >Add two more dedicate virtqueues for datagram sockets,
> >so that it will not unfairly steal resources from
> >stream and future connection-oriented sockets.
> >
> >The two new virtqueues are enabled by default and will
> >be removed if the guest does not support. This will help
> >migration work.
> >
> >btw: enable_dgram argument in vhost_vsock_common_realize
> >is redundant for now, but will be used later when we
> >want to disable DGRAM feature bit for old versions.
> >
> >Signed-off-by: Jiang Wang <jiang.wang@bytedance.com>
> >---
> >v1 -> v2: use qemu cmd option to control number of queues,
> >        removed configuration settings for dgram.
> >v2 -> v3: use ioctl to get features and decide number of
> >        virt queues, instead of qemu cmd option.
> >v3 -> v4: change DGRAM feature bit value to 2. Add an argument
> >        in vhost_vsock_common_realize to indicate dgram is supported or not.
> >v4 -> v5: don't open dev to get vhostfd. Removed leftover definition of
> >        enable_dgram
> >v5 -> v6: fix style errors. Imporve error handling of
> >        vhost_vsock_dgram_supported. Rename MAX_VQS_WITH_DGRAM and another 
> > one.
> >v6 -> v7: Always enable dgram for vhost-user and vhost kernel.
> >        Delete unused virtqueues at the beginning of
> >        vhost_vsock_common_start for migration. Otherwise, migration will 
> > fail.
> >
> > hw/virtio/vhost-user-vsock.c                  |  2 +-
> > hw/virtio/vhost-vsock-common.c                | 32 +++++++++++++++++--
> > hw/virtio/vhost-vsock.c                       |  6 +++-
> > include/hw/virtio/vhost-vsock-common.h        |  6 ++--
> > include/hw/virtio/vhost-vsock.h               |  3 ++
> > include/standard-headers/linux/virtio_vsock.h |  1 +
> > 6 files changed, 43 insertions(+), 7 deletions(-)
> >
> >diff --git a/hw/virtio/vhost-user-vsock.c b/hw/virtio/vhost-user-vsock.c
> >index 6095ed7349..9823a2f3bd 100644
> >--- a/hw/virtio/vhost-user-vsock.c
> >+++ b/hw/virtio/vhost-user-vsock.c
> >@@ -105,7 +105,7 @@ static void vuv_device_realize(DeviceState *dev, Error 
> >**errp)
> >         return;
> >     }
> >
> >-    vhost_vsock_common_realize(vdev, "vhost-user-vsock");
> >+    vhost_vsock_common_realize(vdev, "vhost-user-vsock", true);
> >
> >     vhost_dev_set_config_notifier(&vvc->vhost_dev, &vsock_ops);
> >
> >diff --git a/hw/virtio/vhost-vsock-common.c b/hw/virtio/vhost-vsock-common.c
> >index 4ad6e234ad..7d89b4d242 100644
> >--- a/hw/virtio/vhost-vsock-common.c
> >+++ b/hw/virtio/vhost-vsock-common.c
> >@@ -26,6 +26,18 @@ int vhost_vsock_common_start(VirtIODevice *vdev)
> >     int ret;
> >     int i;
> >
> >+    if (!virtio_has_feature(vdev->guest_features, VIRTIO_VSOCK_F_DGRAM)) {
> >+        struct vhost_virtqueue *vqs;
> >+        virtio_delete_queue(vvc->dgram_recv_vq);
> >+        virtio_delete_queue(vvc->dgram_trans_vq);
> >+
>
> Are you sure it works removing queues here?
> The event_queue would always be #4, but the guest will use #2 which
> we're removing.
>
Yes, this works. In fact, I should include this in v6 and my tests done
in my previous emails have these changes. But before I submitted the patch,
I thought this code was redundant and removed it without further testing.

To explain it, I think the event queue number does not matter for the
vhost and qemu. The vhost-vsock kernel module does not allocate any
data structure for the event queue.  Qemu also only allocates an array of
size 2 or 4 for the tx, rx queues. The event queue is handled separately.

The event queue number only shows up in the spec, but in real code, I don't
see anywhere that the event queue number is used explicitly or implicitly.
The Event queue looks independent of tx, rx queues.

> >+        vqs = vvc->vhost_dev.vqs;
> >+        vvc->vhost_dev.nvqs = MAX_VQS_WITHOUT_DGRAM;
> >+        vvc->vhost_dev.vqs = g_new0(struct vhost_virtqueue,
> >+                                   vvc->vhost_dev.nvqs);
> >+        g_free(vqs);
> >+    }
> >+
> >     if (!k->set_guest_notifiers) {
> >         error_report("binding does not support guest notifiers");
> >         return -ENOSYS;
> >@@ -196,9 +208,11 @@ int vhost_vsock_common_post_load(void *opaque, int 
> >version_id)
> >     return 0;
> > }
> >
> >-void vhost_vsock_common_realize(VirtIODevice *vdev, const char *name)
> >+void vhost_vsock_common_realize(VirtIODevice *vdev, const char *name,
> >+                               bool enable_dgram)
>                                        ^
> It seems always true, and also unused.
>
Yes, I can remove it. I am just wondering when we modify the feature
bit as in your recent seqpacket patch, do we want to change it to false when
the feature is not supported and make the code logically more resonable？
Or do we still make it true even if the feature bit is not supported?

> > {
> >     VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(vdev);
> >+    int nvqs = MAX_VQS_WITH_DGRAM;
> >
> >     virtio_init(vdev, name, VIRTIO_ID_VSOCK,
> >                 sizeof(struct virtio_vsock_config));
> >@@ -209,12 +223,17 @@ void vhost_vsock_common_realize(VirtIODevice *vdev, 
> >const char *name)
> >     vvc->trans_vq = virtio_add_queue(vdev, VHOST_VSOCK_QUEUE_SIZE,
> >                                        vhost_vsock_common_handle_output);
> >
> >+    vvc->dgram_recv_vq = virtio_add_queue(vdev, VHOST_VSOCK_QUEUE_SIZE,
> >+                                          vhost_vsock_common_handle_output);
> >+    vvc->dgram_trans_vq = virtio_add_queue(vdev, VHOST_VSOCK_QUEUE_SIZE,
> >+                                          vhost_vsock_common_handle_output);
> >+
> >     /* The event queue belongs to QEMU */
> >     vvc->event_vq = virtio_add_queue(vdev, VHOST_VSOCK_QUEUE_SIZE,
> >                                        vhost_vsock_common_handle_output);
> >
> >-    vvc->vhost_dev.nvqs = ARRAY_SIZE(vvc->vhost_vqs);
> >-    vvc->vhost_dev.vqs = vvc->vhost_vqs;
> >+    vvc->vhost_dev.nvqs = nvqs;
> >+    vvc->vhost_dev.vqs = g_new0(struct vhost_virtqueue, 
> >vvc->vhost_dev.nvqs);
> >
> >     vvc->post_load_timer = NULL;
> > }
> >@@ -227,6 +246,13 @@ void vhost_vsock_common_unrealize(VirtIODevice *vdev)
> >
> >     virtio_delete_queue(vvc->recv_vq);
> >     virtio_delete_queue(vvc->trans_vq);
> >+    if (vvc->vhost_dev.nvqs == MAX_VQS_WITH_DGRAM) {
> >+        virtio_delete_queue(vvc->dgram_recv_vq);
> >+        virtio_delete_queue(vvc->dgram_trans_vq);
> >+    }
> >+
> >+    g_free(vvc->vhost_dev.vqs);
> >+
> >     virtio_delete_queue(vvc->event_vq);
> >     virtio_cleanup(vdev);
> > }
> >diff --git a/hw/virtio/vhost-vsock.c b/hw/virtio/vhost-vsock.c
> >index 1b1a5c70ed..6e315ecf23 100644
> >--- a/hw/virtio/vhost-vsock.c
> >+++ b/hw/virtio/vhost-vsock.c
> >@@ -23,6 +23,7 @@
> >
> > const int feature_bits[] = {
> >     VIRTIO_VSOCK_F_SEQPACKET,
> >+    VIRTIO_VSOCK_F_DGRAM,
> >     VHOST_INVALID_FEATURE_BIT
> > };
> >
> >@@ -116,6 +117,9 @@ static uint64_t vhost_vsock_get_features(VirtIODevice 
> >*vdev,
> >     VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(vdev);
> >
> >     virtio_add_feature(&requested_features, VIRTIO_VSOCK_F_SEQPACKET);
> >+    if (vvc->vhost_dev.nvqs == MAX_VQS_WITH_DGRAM) {
> >+        virtio_add_feature(&requested_features, VIRTIO_VSOCK_F_DGRAM);
> >+    }
>
> Take a look at
> 20210921161642.206461-1-sgarzare@redhat.com/">https://lore.kernel.org/qemu-devel/20210921161642.206461-1-sgarzare@redhat.com/
>
Yes, I noticed that email. Thanks for reminding me. I did not make
similar changes yet because I want to wait for that patch to be merged.
I can start to make similar changes in the next version.

> If it will be accepted, we should use something similar (e.g.
> `datagram` prop) and handle this flag in vhost-vsock-common.
>
> And we should change a bit the queue handling:
> - if QEMU (new `datagram` prop is `on` or `auto`) and the kernel
>    supports F_DGRAM, we can allocate 5 queues.
Agree with the new prop. But when the kernel supports F_DGRAM, qemu
still only allocates 4 queues. As in the following code：

vvc->vhost_dev.nvqs = nvqs;
vvc->vhost_dev.vqs = g_new0(struct vhost_virtqueue, vvc->vhost_dev.nvqs);

// nvqs will be either 2 or 4. Will not be 5. btw, in the new version, it will
// always be 4.

> - if the guest acked F_DGRAM we can use queue #4 for events, otherwise
>    switch back to queue #2, without removing them.
>
> >     return vhost_get_features(&vvc->vhost_dev, feature_bits,
> >                                 requested_features);
> > }
> >@@ -175,7 +179,7 @@ static void vhost_vsock_device_realize(DeviceState *dev, 
> >Error **errp)
> >         qemu_set_nonblock(vhostfd);
> >     }
> >
> >-    vhost_vsock_common_realize(vdev, "vhost-vsock");
> >+    vhost_vsock_common_realize(vdev, "vhost-vsock", true);
> >
> >     ret = vhost_dev_init(&vvc->vhost_dev, (void *)(uintptr_t)vhostfd,
> >                          VHOST_BACKEND_TYPE_KERNEL, 0, errp);
> >diff --git a/include/hw/virtio/vhost-vsock-common.h 
> >b/include/hw/virtio/vhost-vsock-common.h
> >index e412b5ee98..80151aee35 100644
> >--- a/include/hw/virtio/vhost-vsock-common.h
> >+++ b/include/hw/virtio/vhost-vsock-common.h
> >@@ -27,12 +27,13 @@ enum {
> > struct VHostVSockCommon {
> >     VirtIODevice parent;
> >
> >-    struct vhost_virtqueue vhost_vqs[2];
> >     struct vhost_dev vhost_dev;
> >
> >     VirtQueue *event_vq;
> >     VirtQueue *recv_vq;
> >     VirtQueue *trans_vq;
> >+    VirtQueue *dgram_recv_vq;
> >+    VirtQueue *dgram_trans_vq;
> >
> >     QEMUTimer *post_load_timer;
> > };
> >@@ -41,7 +42,8 @@ int vhost_vsock_common_start(VirtIODevice *vdev);
> > void vhost_vsock_common_stop(VirtIODevice *vdev);
> > int vhost_vsock_common_pre_save(void *opaque);
> > int vhost_vsock_common_post_load(void *opaque, int version_id);
> >-void vhost_vsock_common_realize(VirtIODevice *vdev, const char *name);
> >+void vhost_vsock_common_realize(VirtIODevice *vdev, const char *name,
> >+                                bool enable_dgram);
> > void vhost_vsock_common_unrealize(VirtIODevice *vdev);
> >
> > #endif /* _QEMU_VHOST_VSOCK_COMMON_H */
> >diff --git a/include/hw/virtio/vhost-vsock.h 
> >b/include/hw/virtio/vhost-vsock.h
> >index 84f4e727c7..7d16c0e218 100644
> >--- a/include/hw/virtio/vhost-vsock.h
> >+++ b/include/hw/virtio/vhost-vsock.h
> >@@ -33,4 +33,7 @@ struct VHostVSock {
> >     /*< public >*/
> > };
> >
> >+#define MAX_VQS_WITHOUT_DGRAM 2
> >+#define MAX_VQS_WITH_DGRAM 4
>
> I think was better the naming in the previous version.
>
Sure, will change it back in the next version.

> Thanks,
> Stefano
>