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 <jasowang@xxxxxxxxxx>
---
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
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