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Tsirkin" To: Arseniy Krasnov Cc: Stefan Hajnoczi , Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Jason Wang , Bobby Eshleman , 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 v8 3/4] virtio/vsock: fix logic which reduces credit update messages Message-ID: <20231212110953-mutt-send-email-mst@kernel.org> References: <20231211211658.2904268-1-avkrasnov@salutedevices.com> <20231211211658.2904268-4-avkrasnov@salutedevices.com> <20231212105322-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Dec 12, 2023 at 06:50:39PM +0300, Arseniy Krasnov wrote: > > > On 12.12.2023 18:54, Michael S. Tsirkin wrote: > > On Tue, Dec 12, 2023 at 12:16:57AM +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). > > > > I don't get what does "to stuck both tx and rx sides" mean. > > I meant situation when tx waits for the free space, while rx doesn't send > credit update, just waiting for more data. Sorry for my English :) > > > Besides being agrammatical, is there a way to do this without > > playing with SO_RCVLOWAT? > > No, this may happen only with non-default SO_RCVLOWAT values (e.g. != 1) > > Thanks, Arseniy I am split on whether we need the Fixes tag. I guess if the other side is vhost with SO_RCVLOWAT then it might be stuck and it might apply without SO_RCVLOWAT on the local kernel? > > > >> > >> Fixes: b89d882dc9fc ("vsock/virtio: reduce credit update messages") > >> Signed-off-by: Arseniy Krasnov > >> --- > >> Changelog: > >> v6 -> v7: > >> * Handle wrap of 'fwd_cnt'. > >> * Do to send credit update when 'fwd_cnt' == 'last_fwd_cnt'. > >> v7 -> v8: > >> * Remove unneeded/wrong handling of wrap for 'fwd_cnt'. > >> > >> net/vmw_vsock/virtio_transport_common.c | 13 ++++++++++--- > >> 1 file changed, 10 insertions(+), 3 deletions(-) > >> > >> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > >> index e137d740804e..8572f94bba88 100644 > >> --- a/net/vmw_vsock/virtio_transport_common.c > >> +++ b/net/vmw_vsock/virtio_transport_common.c > >> @@ -558,6 +558,8 @@ 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; > >> + u32 fwd_cnt_delta; > >> + bool low_rx_bytes; > >> int err = -EFAULT; > >> u32 free_space; > >> > >> @@ -601,7 +603,10 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, > >> } > >> } > >> > >> - free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt); > >> + fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt; > >> + free_space = vvs->buf_alloc - fwd_cnt_delta; > >> + low_rx_bytes = (vvs->rx_bytes < > >> + sock_rcvlowat(sk_vsock(vsk), 0, INT_MAX)); > >> > >> spin_unlock_bh(&vvs->rx_lock); > >> > >> @@ -611,9 +616,11 @@ 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 (fwd_cnt_delta && > >> + (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE || low_rx_bytes)) > >> virtio_transport_send_credit_update(vsk); > >> > >> return total; > >> -- > >> 2.25.1 > >