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Message-ID: <20111113174827.GA23310@redhat.com>
Date: Sun, 13 Nov 2011 19:48:28 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Krishna Kumar <krkumar2@...ibm.com>
Cc: rusty@...tcorp.com.au, netdev@...r.kernel.org, kvm@...r.kernel.org,
davem@...emloft.net, virtualization@...ts.linux-foundation.org
Subject: [PATCH RFC] ndo: ndo_queue_xmit/ndo_flush_xmit (was Re: [RFC] [ver3
PATCH 0/6] Implement multiqueue virtio-net)
On Fri, Nov 11, 2011 at 06:32:23PM +0530, Krishna Kumar wrote:
> This patch series resurrects the earlier multiple TX/RX queues
> functionality for virtio_net, and addresses the issues pointed
> out.
I'm guessing the biggest source of contention for transmit is keeping
the TX hardware lock across VM exit. I wonder whether, for transmit,
it's not a good idea to pass all traffic through a single queue to
improve batching, and then if necessary multiplex it out on the host.
The following is a stub at supporting this in the guest - it needs to be
split up, and cleaned up, and I'm not sure about the trick
of returning NETDEV_TX_QUEUED, but should give you the idea.
Compile-tested only, sent out for early flames/feedback.
This is on top of Rusty's unlocked kick patches.
---->
- add optional ndo_queue_xmit/ndo_flush_xmit netdev ops
- ndo_queue_xmit can transmit skb and return NETDEV_TX_OK,
or it can return NETDEV_TX_QUEUED to signal that
the skb was queued and ndo_flush_xmit needs to be called
to actually transmit it.
The point is to improve batching by calling ndo_flush_xmit once after
multiple ndo_queue_xmit calls, and reduce lock contention by calling
ndo_flush_xmit outside any locks.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Compile-tested only.
---
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cbeb586..a7df098 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -105,6 +105,7 @@ struct wireless_dev;
enum netdev_tx {
__NETDEV_TX_MIN = INT_MIN, /* make sure enum is signed */
NETDEV_TX_OK = 0x00, /* driver took care of packet */
+ NETDEV_TX_QUEUED = 0x04, /* queued, need to flush */
NETDEV_TX_BUSY = 0x10, /* driver tx path was busy*/
NETDEV_TX_LOCKED = 0x20, /* driver tx lock was already taken */
};
@@ -712,6 +713,14 @@ struct netdev_tc_txq {
* Must return NETDEV_TX_OK , NETDEV_TX_BUSY.
* (can also return NETDEV_TX_LOCKED iff NETIF_F_LLTX)
* Required can not be NULL.
+ * netdev_tx_t (*ndo_queue_xmit)(struct sk_buff *skb,
+ * struct net_device *dev);
+ * Same as ndo_start_xmit but allows batching packet transmission.
+ * Must return NETDEV_TX_QUEUED , NETDEV_TX_OK , NETDEV_TX_BUSY.
+ * (can also return NETDEV_TX_LOCKED iff NETIF_F_LLTX)
+ *
+ * void (*ndo_flush_xmit)(struct net_device *dev);
+ * Called after queueing a batch of packets.
*
* u16 (*ndo_select_queue)(struct net_device *dev, struct sk_buff *skb);
* Called to decide which queue to when device supports multiple
@@ -863,6 +872,9 @@ struct net_device_ops {
int (*ndo_stop)(struct net_device *dev);
netdev_tx_t (*ndo_start_xmit) (struct sk_buff *skb,
struct net_device *dev);
+ netdev_tx_t (*ndo_queue_xmit)(struct sk_buff *skb,
+ struct net_device *dev);
+ void (*ndo_flush_xmit)(struct net_device *dev);
u16 (*ndo_select_queue)(struct net_device *dev,
struct sk_buff *skb);
void (*ndo_change_rx_flags)(struct net_device *dev,
@@ -2099,6 +2111,10 @@ extern int dev_set_mac_address(struct net_device *,
extern int dev_hard_start_xmit(struct sk_buff *skb,
struct net_device *dev,
struct netdev_queue *txq);
+extern int dev_queue_start_xmit(struct sk_buff *skb,
+ struct net_device *dev,
+ struct netdev_queue *txq);
+extern void dev_flush_start_xmit(struct net_device *dev);
extern int dev_forward_skb(struct net_device *dev,
struct sk_buff *skb);
diff --git a/net/core/dev.c b/net/core/dev.c
index 6ba50a1..608b67c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2167,8 +2167,8 @@ static inline int skb_needs_linearize(struct sk_buff *skb,
!(features & NETIF_F_SG)));
}
-int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
- struct netdev_queue *txq)
+static int __dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
+ struct netdev_queue *txq, bool queue)
{
const struct net_device_ops *ops = dev->netdev_ops;
int rc = NETDEV_TX_OK;
@@ -2224,9 +2224,12 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
}
skb_len = skb->len;
- rc = ops->ndo_start_xmit(skb, dev);
+ if (queue && ops->ndo_queue_xmit)
+ rc = ops->ndo_queue_xmit(skb, dev);
+ else
+ rc = ops->ndo_start_xmit(skb, dev);
trace_net_dev_xmit(skb, rc, dev, skb_len);
- if (rc == NETDEV_TX_OK)
+ if (rc == NETDEV_TX_OK || rc == NETDEV_TX_QUEUED)
txq_trans_update(txq);
return rc;
}
@@ -2246,9 +2249,12 @@ gso:
skb_dst_drop(nskb);
skb_len = nskb->len;
- rc = ops->ndo_start_xmit(nskb, dev);
+ if (queue && ops->ndo_queue_xmit)
+ rc = ops->ndo_queue_xmit(nskb, dev);
+ else
+ rc = ops->ndo_start_xmit(nskb, dev);
trace_net_dev_xmit(nskb, rc, dev, skb_len);
- if (unlikely(rc != NETDEV_TX_OK)) {
+ if (unlikely(rc != NETDEV_TX_OK && rc != NETDEV_TX_QUEUED)) {
if (rc & ~NETDEV_TX_MASK)
goto out_kfree_gso_skb;
nskb->next = skb->next;
@@ -2269,6 +2275,25 @@ out:
return rc;
}
+int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
+ struct netdev_queue *txq)
+{
+ return __dev_hard_start_xmit(skb, dev, txq, false);
+}
+
+int dev_queue_start_xmit(struct sk_buff *skb, struct net_device *dev,
+ struct netdev_queue *txq)
+{
+ return __dev_hard_start_xmit(skb, dev, txq, true);
+}
+
+void dev_flush_start_xmit(struct net_device *dev)
+{
+ const struct net_device_ops *ops = dev->netdev_ops;
+ if (ops->ndo_flush_xmit)
+ ops->ndo_flush_xmit(dev);
+}
+
static u32 hashrnd __read_mostly;
/*
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 69fca27..83b3758 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -102,18 +102,9 @@ static inline int handle_dev_cpu_collision(struct sk_buff *skb,
return ret;
}
-/*
- * Transmit one skb, and handle the return status as required. Holding the
- * __QDISC_STATE_RUNNING bit guarantees that only one CPU can execute this
- * function.
- *
- * Returns to the caller:
- * 0 - queue is empty or throttled.
- * >0 - queue is not empty.
- */
-int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
+static int __sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
struct net_device *dev, struct netdev_queue *txq,
- spinlock_t *root_lock)
+ spinlock_t *root_lock, bool *queued)
{
int ret = NETDEV_TX_BUSY;
@@ -122,10 +113,13 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
HARD_TX_LOCK(dev, txq, smp_processor_id());
if (!netif_tx_queue_frozen_or_stopped(txq))
- ret = dev_hard_start_xmit(skb, dev, txq);
+ ret = dev_queue_start_xmit(skb, dev, txq);
HARD_TX_UNLOCK(dev, txq);
+ if (ret == NETDEV_TX_QUEUED)
+ *queued = true;
+
spin_lock(root_lock);
if (dev_xmit_complete(ret)) {
@@ -150,6 +144,30 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
}
/*
+ * Transmit one skb, and handle the return status as required. Holding the
+ * __QDISC_STATE_RUNNING bit guarantees that only one CPU can execute this
+ * function.
+ *
+ * Returns to the caller:
+ * 0 - queue is empty or throttled.
+ * >0 - queue is not empty.
+ */
+int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
+ struct net_device *dev, struct netdev_queue *txq,
+ spinlock_t *root_lock)
+{
+ bool queued = false;
+ int ret;
+ ret = __sch_direct_xmit(skb, q, dev, txq, root_lock, &queued);
+ if (queued) {
+ spin_unlock(root_lock);
+ dev_flush_start_xmit(dev);
+ spin_lock(root_lock);
+ }
+ return ret;
+}
+
+/*
* NOTE: Called under qdisc_lock(q) with locally disabled BH.
*
* __QDISC_STATE_RUNNING guarantees only one CPU can process
@@ -168,7 +186,7 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
* >0 - queue is not empty.
*
*/
-static inline int qdisc_restart(struct Qdisc *q)
+static inline int qdisc_restart(struct Qdisc *q, bool *queued)
{
struct netdev_queue *txq;
struct net_device *dev;
@@ -184,14 +202,22 @@ static inline int qdisc_restart(struct Qdisc *q)
dev = qdisc_dev(q);
txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
- return sch_direct_xmit(skb, q, dev, txq, root_lock);
+ return __sch_direct_xmit(skb, q, dev, txq, root_lock, queued);
+}
+
+static inline void qdisc_flush_start(struct Qdisc *q)
+{
+ spin_unlock(qdisc_lock(q));
+ dev_flush_start_xmit(qdisc_dev(q));
+ spin_lock(qdisc_lock(q));
}
void __qdisc_run(struct Qdisc *q)
{
int quota = weight_p;
+ bool queued = false;
- while (qdisc_restart(q)) {
+ while (qdisc_restart(q, &queued)) {
/*
* Ordered by possible occurrence: Postpone processing if
* 1. we've exceeded packet quota
@@ -203,6 +229,9 @@ void __qdisc_run(struct Qdisc *q)
}
}
+ if (queued)
+ qdisc_flush_start(q);
+
qdisc_run_end(q);
}
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d6f6f40..6d28c26 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -604,9 +604,11 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
0, skb, GFP_ATOMIC);
}
-static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t __start_xmit(struct sk_buff *skb, struct net_device *dev,
+ bool queue)
{
struct virtnet_info *vi = netdev_priv(dev);
+ bool notify;
int capacity;
/* Free up any pending old buffers before queueing new ones. */
@@ -632,7 +634,12 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
kfree_skb(skb);
return NETDEV_TX_OK;
}
- virtqueue_kick(vi->svq);
+
+ notify = virtqueue_kick_prepare(vi->svq);
+ if (!queue && notify) {
+ virtqueue_notify(vi->svq);
+ notify = false;
+ }
/* Don't wait up for transmitted skbs to be freed. */
skb_orphan(skb);
@@ -652,7 +659,23 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
}
}
- return NETDEV_TX_OK;
+ return notify ? NETDEV_TX_QUEUED : NETDEV_TX_OK;
+}
+
+static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+ return __start_xmit(skb, dev, false);
+}
+
+static netdev_tx_t queue_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+ return __start_xmit(skb, dev, true);
+}
+
+static void flush_xmit(struct net_device *dev)
+{
+ struct virtnet_info *vi = netdev_priv(dev);
+ virtqueue_notify(vi->svq);
}
static int virtnet_set_mac_address(struct net_device *dev, void *p)
@@ -909,6 +932,8 @@ static const struct net_device_ops virtnet_netdev = {
.ndo_open = virtnet_open,
.ndo_stop = virtnet_close,
.ndo_start_xmit = start_xmit,
+ .ndo_queue_xmit = queue_xmit,
+ .ndo_flush_xmit = flush_xmit,
.ndo_validate_addr = eth_validate_addr,
.ndo_set_mac_address = virtnet_set_mac_address,
.ndo_set_rx_mode = virtnet_set_rx_mode,
--
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