Re: [RFC PATCH 1/1] vhost: TX used buffer guest signal accumulation

Shirley Ma
2010-10-28T04:40:04Z

Resubmit this patch for fixing some minor error (white space, typo).

Signed-off-by: Shirley Ma <xma@us.ibm.com>
---
drivers/vhost/net.c | 20 +++++++++++++++++++-
drivers/vhost/vhost.c | 32 ++++++++++++++++++++++++++++++++
drivers/vhost/vhost.h | 3 +++
3 files changed, 54 insertions(+), 1 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 4b4da5b..3eb8016 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -128,6 +128,7 @@ static void handle_tx(struct vhost_net *net)
int err, wmem;
size_t hdr_size;
struct socket *sock;
+ int max_pend = vq->num - (vq->num >> 2);

sock = rcu_dereference_check(vq->private_data,
lockdep_is_held(&vq->mutex));
@@ -198,7 +199,24 @@ static void handle_tx(struct vhost_net *net)
if (err != len)
pr_debug("Truncated TX packet: "
" len %d != %zd\n", err, len);
- vhost_add_used_and_signal(&net->dev, vq, head, 0);
+ /*
+ * if no pending buffer size allocate, signal used buffer
+ * one by one, otherwise, signal used buffer when reaching
+ * 3/4 ring size to reduce CPU utilization.
+ */
+ if (unlikely(vq->pend))
+ vhost_add_used_and_signal(&net->dev, vq, head, 0);
+ else {
+ vq->pend[vq->num_pend].id = head;
+ vq->pend[vq->num_pend].len = 0;
+ ++vq->num_pend;
+ if (vq->num_pend == max_pend) {
+ vhost_add_used_and_signal_n(&net->dev, vq,
+ vq->pend,
+ vq->num_pend);
+ vq->num_pend = 0;
+ }
+ }
total_len += len;
if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
vhost_poll_queue(&vq->poll);
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 94701ff..f2f3288 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -170,6 +170,16 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call_ctx = NULL;
vq->call = NULL;
vq->log_ctx = NULL;
+ /* signal pending used buffers */
+ if (vq->pend) {
+ if (vq->num_pend != 0) {
+ vhost_add_used_and_signal_n(dev, vq, vq->pend,
+ vq->num_pend);
+ vq->num_pend = 0;
+ }
+ kfree(vq->pend);
+ }
+ vq->pend = NULL;
}

static int vhost_worker(void *data)
@@ -273,7 +283,14 @@ long vhost_dev_init(struct vhost_dev *dev,
dev->vqs[i].heads = NULL;
dev->vqs[i].dev = dev;
mutex_init(&dev->vqs[i].mutex);
+ dev->vqs[i].num_pend = 0;
+ dev->vqs[i].pend = NULL;
vhost_vq_reset(dev, dev->vqs + i);
+ /* signal 3/4 of ring size used buffers */
+ dev->vqs[i].pend = kmalloc((dev->vqs[i].num -
+ (dev->vqs[i].num >> 2)) *
+ sizeof *dev->vqs[i].pend,
+ GFP_KERNEL);
if (dev->vqs[i].handle_kick)
vhost_poll_init(&dev->vqs[i].poll,
dev->vqs[i].handle_kick, POLLIN, dev);
@@ -599,6 +616,21 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
r = -EINVAL;
break;
}
+ if (vq->num != s.num) {
+ /* signal used buffers first */
+ if (vq->pend) {
+ if (vq->num_pend != 0) {
+ vhost_add_used_and_signal_n(vq->dev, vq,
+ vq->pend,
+ vq->num_pend);
+ vq->num_pend = 0;
+ }
+ kfree(vq->pend);
+ }
+ /* realloc pending used buffers size */
+ vq->pend = kmalloc((s.num - (s.num >> 2)) *
+ sizeof *vq->pend, GFP_KERNEL);
+ }
vq->num = s.num;
break;
case VHOST_SET_VRING_BASE:
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 073d06a..78949c0 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -108,6 +108,9 @@ struct vhost_virtqueue {
/* Log write descriptors */
void __user *log_base;
struct vhost_log *log;
+ /* delay multiple used buffers to signal once */
+ int num_pend;
+ struct vring_used_elem *pend;
};

struct vhost_dev {