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Message-ID: <v335g4fjrn5f6tsw4nysztaklze2obnjwpezps3jgb2xickpge@ea5woxob52nc>
Date: Tue, 5 Dec 2023 11:54:37 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Arseniy Krasnov <avkrasnov@...utedevices.com>
Cc: Stefan Hajnoczi <stefanha@...hat.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
Bobby Eshleman <bobby.eshleman@...edance.com>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kernel@...rdevices.ru,
oxffffaa@...il.com
Subject: Re: [PATCH net-next v6 3/4] virtio/vsock: fix logic which reduces
credit update messages
On Tue, Dec 05, 2023 at 09:48:05AM +0300, Arseniy Krasnov wrote:
>Add one more condition for sending credit update during dequeue from
>stream socket: when number of bytes in the rx queue is smaller than
>SO_RCVLOWAT value of the socket. This is actual for non-default value
>of SO_RCVLOWAT (e.g. not 1) - idea is to "kick" peer to continue data
>transmission, because we need at least SO_RCVLOWAT bytes in our rx
>queue to wake up user for reading data (in corner case it is also
>possible to stuck both tx and rx sides, this is why 'Fixes' is used).
>
>Fixes: b89d882dc9fc ("vsock/virtio: reduce credit update messages")
>Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
>---
> net/vmw_vsock/virtio_transport_common.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index e137d740804e..461c89882142 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -558,6 +558,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> struct virtio_vsock_sock *vvs = vsk->trans;
> size_t bytes, total = 0;
> struct sk_buff *skb;
>+ bool low_rx_bytes;
> int err = -EFAULT;
> u32 free_space;
>
>@@ -602,6 +603,8 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> }
>
> free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
>+ low_rx_bytes = (vvs->rx_bytes <
>+ sock_rcvlowat(sk_vsock(vsk), 0, INT_MAX));
As in the previous patch, should we avoid the update it if `fwd_cnt` and
`last_fwd_cnt` are the same?
Now I'm thinking if it is better to add that check directly in
virtio_transport_send_credit_update().
Stefano
>
> spin_unlock_bh(&vvs->rx_lock);
>
>@@ -611,9 +614,11 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> * too high causes extra messages. Too low causes transmitter
> * stalls. As stalls are in theory more expensive than extra
> * messages, we set the limit to a high value. TODO: experiment
>- * with different values.
>+ * with different values. Also send credit update message when
>+ * number of bytes in rx queue is not enough to wake up reader.
> */
>- if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
>+ if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE ||
>+ low_rx_bytes)
> virtio_transport_send_credit_update(vsk);
>
> return total;
>--
>2.25.1
>
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