From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: [PATCH net-next rfc V2 2/2] vhost_net: basic polling support Date: Thu, 29 Oct 2015 04:45:26 -0400 Message-ID: <1446108326-37765-3-git-send-email-jasowang@redhat.com> References: <1446108326-37765-1-git-send-email-jasowang@redhat.com> Cc: Jason Wang To: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1446108326-37765-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.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. Signed-off-by: Jason Wang --- drivers/vhost/net.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 50 insertions(+), 4 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 9eda69e..30e6d3d 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -31,9 +31,13 @@ #include "vhost.h" static int experimental_zcopytx = 1; +static int busyloop_timeout = 50; module_param(experimental_zcopytx, int, 0444); MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;" " 1 -Enable; 0 - Disable"); +module_param(busyloop_timeout, int, 0444); +MODULE_PARM_DESC(busyloop_timeout, "Maximum number of time (in us) " + "could be spend on busy polling"); /* Max number of bytes transferred before requeueing the job. * Using this limit prevents one virtqueue from starving others. */ @@ -287,6 +291,49 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) rcu_read_unlock_bh(); } +static inline unsigned long busy_clock(void) +{ + return local_clock() >> 10; +} + +static bool tx_can_busy_poll(struct vhost_dev *dev, + unsigned long endtime) +{ + return likely(!need_resched()) && + likely(!time_after(busy_clock(), endtime)) && + likely(!signal_pending(current)) && + !vhost_has_work(dev) && + single_task_running(); +} + +static int vhost_net_tx_get_vq_desc(struct vhost_virtqueue *vq, + struct iovec iov[], unsigned int iov_size, + unsigned int *out_num, unsigned int *in_num) +{ + unsigned long uninitialized_var(endtime); + int head; + + if (busyloop_timeout) { + preempt_disable(); + endtime = busy_clock() + busyloop_timeout; + } + +again: + head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), + out_num, in_num, NULL, NULL); + + if (head == vq->num && busyloop_timeout && + tx_can_busy_poll(vq->dev, endtime)) { + cpu_relax(); + goto again; + } + + if (busyloop_timeout) + preempt_enable(); + + return head; +} + /* 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) @@ -331,10 +378,9 @@ static void handle_tx(struct vhost_net *net) % UIO_MAXIOV == nvq->done_idx)) break; - head = vhost_get_vq_desc(vq, vq->iov, - ARRAY_SIZE(vq->iov), - &out, &in, - NULL, NULL); + head = vhost_net_tx_get_vq_desc(vq, vq->iov, + ARRAY_SIZE(vq->iov), + &out, &in); /* On error, stop handling until the next kick. */ if (unlikely(head < 0)) break; -- 1.8.3.1