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Subject[PATCH net 1/4] vhost: introduce vhost_exceeds_weight()
Date
We used to have vhost_exceeds_weight() for vhost-net to:

- prevent vhost kthread from hogging the cpu
- balance the time spent between TX and RX

This function could be useful for vsock and scsi as well. So move it
to vhost.c. Device must specify a weight which counts the number of
requests, or it can also specific a byte_weight which counts the
number of bytes that has been processed.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/net.c | 22 ++++++----------------
drivers/vhost/scsi.c | 9 ++++++++-
drivers/vhost/vhost.c | 20 +++++++++++++++++++-
drivers/vhost/vhost.h | 5 ++++-
drivers/vhost/vsock.c | 12 +++++++++++-
5 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index df51a35..061a06d 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -604,12 +604,6 @@ static size_t init_iov_iter(struct vhost_virtqueue *vq, struct iov_iter *iter,
return iov_iter_count(iter);
}

-static bool vhost_exceeds_weight(int pkts, int total_len)
-{
- return total_len >= VHOST_NET_WEIGHT ||
- pkts >= VHOST_NET_PKT_WEIGHT;
-}
-
static int get_tx_bufs(struct vhost_net *net,
struct vhost_net_virtqueue *nvq,
struct msghdr *msg,
@@ -845,10 +839,8 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
vq->heads[nvq->done_idx].len = 0;
++nvq->done_idx;
- if (vhost_exceeds_weight(++sent_pkts, total_len)) {
- vhost_poll_queue(&vq->poll);
+ if (vhost_exceeds_weight(vq, ++sent_pkts, total_len))
break;
- }
}

vhost_tx_batch(net, nvq, sock, &msg);
@@ -951,10 +943,9 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
else
vhost_zerocopy_signal_used(net, vq);
vhost_net_tx_packet(net);
- if (unlikely(vhost_exceeds_weight(++sent_pkts, total_len))) {
- vhost_poll_queue(&vq->poll);
+ if (unlikely(vhost_exceeds_weight(vq, ++sent_pkts,
+ total_len)))
break;
- }
}
}

@@ -1239,10 +1230,8 @@ static void handle_rx(struct vhost_net *net)
vhost_log_write(vq, vq_log, log, vhost_len,
vq->iov, in);
total_len += vhost_len;
- if (unlikely(vhost_exceeds_weight(++recv_pkts, total_len))) {
- vhost_poll_queue(&vq->poll);
+ if (unlikely(vhost_exceeds_weight(vq, ++recv_pkts, total_len)))
goto out;
- }
}
if (unlikely(busyloop_intr))
vhost_poll_queue(&vq->poll);
@@ -1338,7 +1327,8 @@ static int vhost_net_open(struct inode *inode, struct file *f)
vhost_net_buf_init(&n->vqs[i].rxq);
}
vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX,
- UIO_MAXIOV + VHOST_NET_BATCH);
+ UIO_MAXIOV + VHOST_NET_BATCH,
+ VHOST_NET_WEIGHT, VHOST_NET_PKT_WEIGHT);

vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, EPOLLOUT, dev);
vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, EPOLLIN, dev);
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 618fb64..d830579 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -57,6 +57,12 @@
#define VHOST_SCSI_PREALLOC_UPAGES 2048
#define VHOST_SCSI_PREALLOC_PROT_SGLS 2048

+/* Max number of requests before requeueing the job.
+ * Using this limit prevents one virtqueue from starving others with
+ * request.
+ */
+#define VHOST_SCSI_WEIGHT 256
+
struct vhost_scsi_inflight {
/* Wait for the flush operation to finish */
struct completion comp;
@@ -1622,7 +1628,8 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
vqs[i] = &vs->vqs[i].vq;
vs->vqs[i].vq.handle_kick = vhost_scsi_handle_kick;
}
- vhost_dev_init(&vs->dev, vqs, VHOST_SCSI_MAX_VQ, UIO_MAXIOV);
+ vhost_dev_init(&vs->dev, vqs, VHOST_SCSI_MAX_VQ, UIO_MAXIOV,
+ VHOST_SCSI_WEIGHT, 0);

vhost_scsi_init_inflight(vs, NULL);

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 351af88..290d6e5 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -413,8 +413,24 @@ static void vhost_dev_free_iovecs(struct vhost_dev *dev)
vhost_vq_free_iovecs(dev->vqs[i]);
}

+bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
+ int pkts, int total_len)
+{
+ struct vhost_dev *dev = vq->dev;
+
+ if ((dev->byte_weight && total_len >= dev->byte_weight) ||
+ pkts >= dev->weight) {
+ vhost_poll_queue(&vq->poll);
+ return true;
+ }
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(vhost_exceeds_weight);
+
void vhost_dev_init(struct vhost_dev *dev,
- struct vhost_virtqueue **vqs, int nvqs, int iov_limit)
+ struct vhost_virtqueue **vqs, int nvqs,
+ int iov_limit, int weight, int byte_weight)
{
struct vhost_virtqueue *vq;
int i;
@@ -428,6 +444,8 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->mm = NULL;
dev->worker = NULL;
dev->iov_limit = iov_limit;
+ dev->weight = weight;
+ dev->byte_weight = byte_weight;
init_llist_head(&dev->work_list);
init_waitqueue_head(&dev->wait);
INIT_LIST_HEAD(&dev->read_list);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 9490e7d..27a78a9 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -171,10 +171,13 @@ struct vhost_dev {
struct list_head pending_list;
wait_queue_head_t wait;
int iov_limit;
+ int weight;
+ int byte_weight;
};

+bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);
void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs,
- int nvqs, int iov_limit);
+ int nvqs, int iov_limit, int weight, int byte_weight);
long vhost_dev_set_owner(struct vhost_dev *dev);
bool vhost_dev_has_owner(struct vhost_dev *dev);
long vhost_dev_check_owner(struct vhost_dev *);
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index bb5fc0e..47c6d4d 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -21,6 +21,14 @@
#include "vhost.h"

#define VHOST_VSOCK_DEFAULT_HOST_CID 2
+/* Max number of bytes transferred before requeueing the job.
+ * Using this limit prevents one virtqueue from starving others. */
+#define VHOST_VSOCK_WEIGHT 0x80000
+/* Max number of packets transferred before requeueing the job.
+ * Using this limit prevents one virtqueue from starving others with
+ * small pkts.
+ */
+#define VHOST_VSOCK_PKT_WEIGHT 256

enum {
VHOST_VSOCK_FEATURES = VHOST_FEATURES,
@@ -531,7 +539,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
vsock->vqs[VSOCK_VQ_TX].handle_kick = vhost_vsock_handle_tx_kick;
vsock->vqs[VSOCK_VQ_RX].handle_kick = vhost_vsock_handle_rx_kick;

- vhost_dev_init(&vsock->dev, vqs, ARRAY_SIZE(vsock->vqs), UIO_MAXIOV);
+ vhost_dev_init(&vsock->dev, vqs, ARRAY_SIZE(vsock->vqs),
+ UIO_MAXIOV, VHOST_VSOCK_PKT_WEIGHT,
+ VHOST_VSOCK_WEIGHT);

file->private_data = vsock;
spin_lock_init(&vsock->send_pkt_list_lock);
--
1.8.3.1
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