From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: [PATCH net-next RFC 2/2] vhost_net: basic polling support Date: Thu, 22 Oct 2015 01:27:29 -0400 Message-ID: <1445491649-62614-2-git-send-email-jasowang@redhat.com> References: <1445491649-62614-1-git-send-email-jasowang@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1445491649-62614-1-git-send-email-jasowang@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: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org This patch tries to poll for new added tx buffer for a while at the end of tx processing. The maximum time spent on polling were limited through a module parameter. To avoid block rx, the loop will end it there's new other works queued on vhost so in fact socket receive queue is also be polled. busyloop_timeout = 50 gives us following improvement on TCP_RR test: size/session/+thu%/+normalize% 1/ 1/ +5%/ -20% 1/ 50/ +17%/ +3% Signed-off-by: Jason Wang --- drivers/vhost/net.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 9eda69e..bbb522a 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -31,7 +31,9 @@ #include "vhost.h" static int experimental_zcopytx = 1; +static int busyloop_timeout = 50; module_param(experimental_zcopytx, int, 0444); +module_param(busyloop_timeout, int, 0444); MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;" " 1 -Enable; 0 - Disable"); @@ -287,12 +289,23 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) rcu_read_unlock_bh(); } +static bool tx_can_busy_poll(struct vhost_dev *dev, + unsigned long endtime) +{ + unsigned long now = local_clock() >> 10; + + return busyloop_timeout && !need_resched() && + !time_after(now, endtime) && !vhost_has_work(dev) && + single_task_running(); +} + /* Expects to be always run from workqueue - which acts as * read-size critical section for our kind of RCU. */ static void handle_tx(struct vhost_net *net) { struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX]; struct vhost_virtqueue *vq = &nvq->vq; + unsigned long endtime; unsigned out, in; int head; struct msghdr msg = { @@ -331,6 +344,8 @@ static void handle_tx(struct vhost_net *net) % UIO_MAXIOV == nvq->done_idx)) break; + endtime = (local_clock() >> 10) + busyloop_timeout; +again: head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in, @@ -340,6 +355,10 @@ static void handle_tx(struct vhost_net *net) break; /* Nothing new? Wait for eventfd to tell us they refilled. */ if (head == vq->num) { + if (tx_can_busy_poll(vq->dev, endtime)) { + cpu_relax(); + goto again; + } if (unlikely(vhost_enable_notify(&net->dev, vq))) { vhost_disable_notify(&net->dev, vq); continue; -- 1.8.3.1