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[79.36.61.170]) by smtp.gmail.com with ESMTPSA id v8sm34676506wra.79.2019.09.03.00.31.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Sep 2019 00:31:23 -0700 (PDT) Date: Tue, 3 Sep 2019 09:31:20 +0200 From: Stefano Garzarella To: "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Stefan Hajnoczi , "David S. Miller" , virtualization@lists.linux-foundation.org, Jason Wang , kvm@vger.kernel.org Subject: Re: [PATCH v4 2/5] vsock/virtio: reduce credit update messages Message-ID: <20190903073120.kefllalytkvidcvh@steredhat> References: <20190717113030.163499-1-sgarzare@redhat.com> <20190717113030.163499-3-sgarzare@redhat.com> <20190903003050-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190903003050-mutt-send-email-mst@kernel.org> User-Agent: NeoMutt/20180716 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Sep 03, 2019 at 12:38:02AM -0400, Michael S. Tsirkin wrote: > 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. > */ > Yes, it is better, sorry for that. I'll try to avoid unnecessary comments, explaining the reason for certain changes. Since this patch is already queued in net-next, should I send another patch to fix the comment? Thanks, Stefano