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 <jasowang@xxxxxxxxxx>
---
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
--
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