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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 v7 3/4] virtio/vsock: fix logic which reduces credit update messages Message-ID: <20231206165045-mutt-send-email-mst@kernel.org> References: <20231206211849.2707151-1-avkrasnov@salutedevices.com> <20231206211849.2707151-4-avkrasnov@salutedevices.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231206211849.2707151-4-avkrasnov@salutedevices.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 07, 2023 at 12:18:48AM +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). > Also handle case when 'fwd_cnt' wraps, while 'last_fwd_cnt' is still > not. > > 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'. > > net/vmw_vsock/virtio_transport_common.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > index e137d740804e..39f8660d825d 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 +603,15 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, > } > } > > - free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt); > + /* Handle wrap of 'fwd_cnt'. */ > + if (vvs->fwd_cnt < vvs->last_fwd_cnt) > + fwd_cnt_delta = vvs->fwd_cnt + (U32_MAX - vvs->last_fwd_cnt); Are you sure there's no off by one here? for example if fwd_cnt is 0 and last_fwd_cnt is 0xfffffffff then apparently delta is 0. > + else > + fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt; I actually don't see what is wrong with just fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt 32 bit unsigned math will I think handle wrap around correctly. And given buf_alloc is also u32 - I don't see where the bug is in the original code. > + > + 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 +621,11 @@ 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