On Wed, Jun 23, 2021 at 11:50:33PM -0700, Jiang Wang . wrote:
Hi Stefano,
I checked virtio_net_set_multiqueue(), which will help with following
changes in my patch:
#ifdef CONFIG_VHOST_VSOCK_DGRAM
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);
#endif
But I think there is still an issue with the following lines, right?
Yep, I think so.
#ifdef CONFIG_VHOST_VSOCK_DGRAM
struct vhost_virtqueue vhost_vqs[4];
#else
struct vhost_virtqueue vhost_vqs[2];
#endif
I think the problem with feature bits is that they are set and get after
vhost_vsock_common_realize() and after vhost_dev_init() in drivers/vhost/vsock.c
But those virtqueues need to be set up correctly beforehand.
I think we can follow net and scsi vhost devices, so we can set a
VHOST_VSOCK_VQ_MAX(5), allocates all the queues in any case and then use
only the queues acked by the guest.
I tried to test with the host kernel allocating 4 vqs, but qemu only
allocated 2 vqs, and
guest kernel will not be able to send even the vsock stream packets. I
think the host
kernel and the qemu have to agree on the number of vhost_vqs. Do you agree?
Did I miss something?
Mmm, I need to check, but for example vhost-net calls vhost_dev_init()
with VHOST_NET_VQ_MAX, but then the guest can decide to use only one
couple of TX and RX queues.
I'm not sure about qemu point of view, but I expected that QEMU can set
less queues then queues allocated by the kernel. `vhost_dev.nvqs` should
be set with the amount of queue that QEMU can handle.
Another idea to make the setting in runtime instead of compiling time
is to use
qemu cmd-line options, then qemu can allocate 2 or 4 queues depending
on
the cmd line. This will solve the issue when the host kernel is an old
one( no dgram
support) and the qemu is a new one.
I don't think this is a good idea, at most we can add an ioctl that qemu
can use to query the kernel about allocated queues, but I still need to
understand better if we really we need this.
But there is still an issue when the host kernel is a new one, while
the qemu
is an old one. I am not sure how to make the virtqueues numbers to
change in run-time
for the host kernel. In another email thread, you mentioned removing kconfig
in the linux kernel, I believe that is related to this qemu patch,
right?
It was related to both, I don't think we should build QEMU and Linux
with or without dgram support.
If so,
any ideas that I can make the host kernel change the number of vqs in
the run-time
or when starting up vsock? The only way I can think of is to use a
kernel module parameter
for the vsock_vhost module. Any other ideas? Thanks.
I need to check better, but we should be able to do all at run time
looking at the features field. As I said, both QEMU and kernel can
allocate the maximum number of queues that they can handle, then enable
only the queues allocated by the guest (e.g. during
vhost_vsock_common_start()).
btw, I searched Linux kernel code but did not find any examples.
I'm a bit busy this week, I'll try to write some PoC next week if you
can't find a working solution. (without any #ifdef :-)
Thanks,
Stefano
