From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v4 2/5] vsock/virtio: reduce credit update messages Date: Tue, 3 Sep 2019 00:38:02 -0400 Message-ID: <20190903003050-mutt-send-email-mst@kernel.org> References: <20190717113030.163499-1-sgarzare@redhat.com> <20190717113030.163499-3-sgarzare@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20190717113030.163499-3-sgarzare@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Stefano Garzarella Cc: kvm@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Stefan Hajnoczi , "David S. Miller" List-Id: virtualization@lists.linuxfoundation.org On Wed, Jul 17, 2019 at 01:30:27PM +0200, Stefano Garzarella wrote: > In order to reduce the number of credit update messages, > we send them only when the space available seen by the > transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE. > > Signed-off-by: Stefano Garzarella > --- > include/linux/virtio_vsock.h | 1 + > net/vmw_vsock/virtio_transport_common.c | 16 +++++++++++++--- > 2 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h > index 7d973903f52e..49fc9d20bc43 100644 > --- a/include/linux/virtio_vsock.h > +++ b/include/linux/virtio_vsock.h > @@ -41,6 +41,7 @@ struct virtio_vsock_sock { > > /* Protected by rx_lock */ > u32 fwd_cnt; > + u32 last_fwd_cnt; > u32 rx_bytes; > struct list_head rx_queue; > }; > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c > index 095221f94786..a85559d4d974 100644 > --- a/net/vmw_vsock/virtio_transport_common.c > +++ b/net/vmw_vsock/virtio_transport_common.c > @@ -211,6 +211,7 @@ static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs, > void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt) > { > spin_lock_bh(&vvs->tx_lock); > + vvs->last_fwd_cnt = vvs->fwd_cnt; > pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt); > pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc); > spin_unlock_bh(&vvs->tx_lock); > @@ -261,6 +262,7 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, > struct virtio_vsock_sock *vvs = vsk->trans; > struct virtio_vsock_pkt *pkt; > size_t bytes, total = 0; > + u32 free_space; > int err = -EFAULT; > > spin_lock_bh(&vvs->rx_lock); > @@ -291,11 +293,19 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk, > virtio_transport_free_pkt(pkt); > } > } > + > + free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt); > + > spin_unlock_bh(&vvs->rx_lock); > > - /* Send a credit pkt to peer */ > - virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM, > - NULL); > + /* We send a credit update only when the space available seen > + * by the transmitter is less than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE This is just repeating what code does though. Please include the *reason* for the condition. E.g. here's a better comment: /* To reduce number of credit update messages, * don't update credits as long as lots of space is available. * Note: the limit chosen here is arbitrary. Setting the limit * 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. */ > + */ > + if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) { > + virtio_transport_send_credit_update(vsk, > + VIRTIO_VSOCK_TYPE_STREAM, > + NULL); > + } > > return total; > > -- > 2.20.1