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Date:   Mon, 11 Dec 2023 13:09:32 +0100
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Arseniy Krasnov <avkrasnov@salutedevices.com>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel@sberdevices.ru, oxffffaa@gmail.com
Subject: Re: [PATCH net-next v7 2/4] virtio/vsock: send credit update during
 setting SO_RCVLOWAT
Message-ID: <5b6duib6nre43ak5kzjgtfrnov5ogd4clka2hgf2xlgpm4jmw7@wbm4jxxslrm6>
References: <20231206211849.2707151-1-avkrasnov@salutedevices.com>
 <20231206211849.2707151-3-avkrasnov@salutedevices.com>
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In-Reply-To: <20231206211849.2707151-3-avkrasnov@salutedevices.com>
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On Thu, Dec 07, 2023 at 12:18:47AM +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@salutedevices.com>
>---
> 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.
> v5 -> v6:
>  * Reorder callbacks in transport structures.
>  * Do to send credit update when 'fwd_cnt' == 'last_fwd_cnt'.
>
> 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 | 30 +++++++++++++++++++++++++
> net/vmw_vsock/vsock_loopback.c          |  1 +
> 5 files changed, 34 insertions(+)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index f75731396b7e..ec20ecff85c7 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -449,6 +449,7 @@ static struct virtio_transport vhost_transport = {
> 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>
> 		.read_skb = virtio_transport_read_skb,
> 	},
>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..f495b9e5186b 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -537,6 +537,7 @@ static struct virtio_transport virtio_transport = {
> 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>
> 		.read_skb = virtio_transport_read_skb,
> 	},
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index f6dc896bf44c..e137d740804e 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1684,6 +1684,36 @@ 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. Also
>+	 * don't send credit update when peer already knows actual value -
>+	 * such transmission will be useless.
>+	 */
>+	send_update = (vvs->rx_bytes < val) &&
>+		      (vvs->fwd_cnt != vvs->last_fwd_cnt);
>+
>+	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;
>+}
>+EXPORT_SYMBOL_GPL(virtio_transport_notify_set_rcvlowat);
>+
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Asias He");
> MODULE_DESCRIPTION("common code for virtio vsock");
>diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
>index 048640167411..6dea6119f5b2 100644
>--- a/net/vmw_vsock/vsock_loopback.c
>+++ b/net/vmw_vsock/vsock_loopback.c
>@@ -96,6 +96,7 @@ static struct virtio_transport loopback_transport = {
> 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
> 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
> 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
>+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
>
> 		.read_skb = virtio_transport_read_skb,
> 	},
>-- 
>2.25.1
>