On Thu, Nov 30, 2023 at 06:41:56PM +0300, Arseniy Krasnov wrote: > > > On 30.11.2023 17:11, Stefano Garzarella wrote: > > On Thu, Nov 30, 2023 at 08:58:58AM -0500, Michael S. Tsirkin wrote: > >> On Thu, Nov 30, 2023 at 04:43:34PM +0300, Arseniy Krasnov wrote: > >>> > >>> > >>> On 30.11.2023 16:42, Michael S. Tsirkin wrote: > >>> > On Thu, Nov 30, 2023 at 04:08:39PM +0300, Arseniy Krasnov wrote: > >>> >> Send credit update message when SO_RCVLOWAT is updated and it is bigger > >>> >> than number of bytes in rx queue. It is needed, because 'poll()' will > >>> >> wait until number of bytes in rx queue will be not smaller than > >>> >> SO_RCVLOWAT, so kick sender to send more data. Otherwise mutual hungup > >>> >> for tx/rx is possible: sender waits for free space and receiver is > >>> >> waiting data in 'poll()'. > >>> >> > >>> >> Signed-off-by: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx> > >>> >> --- > >>> >> Changelog: > >>> >> v1 -> v2: > >>> >> * Update commit message by removing 'This patch adds XXX' manner. > >>> >> * Do not initialize 'send_update' variable - set it directly during > >>> >> first usage. > >>> >> v3 -> v4: > >>> >> * Fit comment in 'virtio_transport_notify_set_rcvlowat()' to 80 chars. > >>> >> v4 -> v5: > >>> >> * Do not change callbacks order in transport structures. > >>> >> > >>> >> drivers/vhost/vsock.c | 1 + > >>> >> include/linux/virtio_vsock.h | 1 + > >>> >> net/vmw_vsock/virtio_transport.c | 1 + > >>> >> net/vmw_vsock/virtio_transport_common.c | 27 +++++++++++++++++++++++++ > >>> >> net/vmw_vsock/vsock_loopback.c | 1 + > >>> >> 5 files changed, 31 insertions(+) > >>> >> > >>> >> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c > >>> >> index f75731396b7e..4146f80db8ac 100644 > >>> >> --- a/drivers/vhost/vsock.c > >>> >> +++ b/drivers/vhost/vsock.c > >>> >> @@ -451,6 +451,7 @@ static struct virtio_transport vhost_transport = { > >>> >> .notify_buffer_size = virtio_transport_notify_buffer_size, > >>> >> > >>> >> .read_skb = virtio_transport_read_skb, > >>> >> + .notify_set_rcvlowat = virtio_transport_notify_set_rcvlowat > >>> >> }, > >>> >> > >>> >> .send_pkt = vhost_transport_send_pkt, > >>> >> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h > >>> >> index ebb3ce63d64d..c82089dee0c8 100644 > >>> >> --- a/include/linux/virtio_vsock.h > >>> >> +++ b/include/linux/virtio_vsock.h > >>> >> @@ -256,4 +256,5 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit); > >>> >> void virtio_transport_deliver_tap_pkt(struct sk_buff *skb); > >>> >> int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list); > >>> >> int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor); > >>> >> +int virtio_transport_notify_set_rcvlowat(struct vsock_sock *vsk, int val); > >>> >> #endif /* _LINUX_VIRTIO_VSOCK_H */ > >>> >> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c > >>> >> index af5bab1acee1..8007593a3a93 100644 > >>> >> --- a/net/vmw_vsock/virtio_transport.c > >>> >> +++ b/net/vmw_vsock/virtio_transport.c > >>> >> @@ -539,6 +539,7 @@ static struct virtio_transport virtio_transport = { > >>> >> .notify_buffer_size = virtio_transport_notify_buffer_size, > >>> >> > >>> >> .read_skb = virtio_transport_read_skb, > >>> >> + .notify_set_rcvlowat = virtio_transport_notify_set_rcvlowat > >>> >> }, > >>> >> > >>> >> .send_pkt = virtio_transport_send_pkt, > >>> >> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > >>> >> index f6dc896bf44c..1cb556ad4597 100644 > >>> >> --- a/net/vmw_vsock/virtio_transport_common.c > >>> >> +++ b/net/vmw_vsock/virtio_transport_common.c > >>> >> @@ -1684,6 +1684,33 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto > >>> >> } > >>> >> EXPORT_SYMBOL_GPL(virtio_transport_read_skb); > >>> >> > >>> >> +int virtio_transport_notify_set_rcvlowat(struct vsock_sock *vsk, >> int val) > >>> >> +{ > >>> >> + struct virtio_vsock_sock *vvs = vsk->trans; > >>> >> + bool send_update; > >>> >> + > >>> >> + spin_lock_bh(&vvs->rx_lock); > >>> >> + > >>> >> + /* If number of available bytes is less than new SO_RCVLOWAT value, > >>> >> + * kick sender to send more data, because sender may sleep in >> its > >>> >> + * 'send()' syscall waiting for enough space at our side. > >>> >> + */ > >>> >> + send_update = vvs->rx_bytes < val; > >>> >> + > >>> >> + spin_unlock_bh(&vvs->rx_lock); > >>> >> + > >>> >> + if (send_update) { > >>> >> + int err; > >>> >> + > >>> >> + err = virtio_transport_send_credit_update(vsk); > >>> >> + if (err < 0) > >>> >> + return err; > >>> >> + } > >>> >> + > >>> >> + return 0; > >>> >> +} > >>> > > >>> > > >>> > I find it strange that this will send a credit update > >>> > even if nothing changed since this was called previously. > >>> > I'm not sure whether this is a problem protocol-wise, > >>> > but it certainly was not envisioned when the protocol was > >>> > built. WDYT? > >>> > >>> >From virtio spec I found: > >>> > >>> It is also valid to send a VIRTIO_VSOCK_OP_CREDIT_UPDATE packet without previously receiving a > >>> VIRTIO_VSOCK_OP_CREDIT_REQUEST packet. This allows communicating updates any time a change > >>> in buffer space occurs. > >>> So I guess there is no limitations to send such type of packet, e.g. it is not > >>> required to be a reply for some another packet. Please, correct me if im wrong. > >>> > >>> Thanks, Arseniy > >> > >> > >> Absolutely. My point was different - with this patch it is possible > >> that you are not adding any credits at all since the previous > >> VIRTIO_VSOCK_OP_CREDIT_UPDATE. > > > > I think the problem we're solving here is that since as an optimization we avoid sending the update for every byte we consume, but we put a threshold, then we make sure we update the peer. > > > > A credit update contains a snapshot and sending it the same as the previous one should not create any problem. > > > > My doubt now is that we only do this when we set RCVLOWAT , should we also do something when we consume bytes to avoid the optimization we have? > > @Michael, Stefano just reproduced problem during bytes reading, but there is already old fix for this, which we forget to merge:) > I think it must be included to this patchset. > > https://lore.kernel.org/netdev/f304eabe-d2ef-11b1-f115-6967632f0339@xxxxxxxxxxxxxx/ > > Thanks, Arseniy I generally don't merge patches tagged as RFC. Repost without that tag? Also, it looks like a bugfix we need either way, no? > > > > Stefano > >