net/sched: Add HW offloading capability to ETF

Add infra so etf qdisc supports HW offload of time-based transmission.

For hw offload, the time sorted list is still used, so packets are
dequeued always in order of txtime.

Example:

$ tc qdisc replace dev enp2s0 parent root handle 100 mqprio num_tc 3 \
           map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 queues 1@0 1@1 2@2 hw 0

$ tc qdisc add dev enp2s0 parent 100:1 etf offload delta 100000 \
	   clockid CLOCK_REALTIME

In this example, the Qdisc will use HW offload for the control of the
transmission time through the network adapter. The hrtimer used for
packets scheduling inside the qdisc will use the clockid CLOCK_REALTIME
as reference and packets leave the Qdisc "delta" (100000) nanoseconds
before their transmission time. Because this will be using HW offload and
since dynamic clocks are not supported by the hrtimer, the system clock
and the PHC clock must be synchronized for this mode to behave as
expected.

Signed-off-by: Jesus Sanchez-Palencia <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Jesus Sanchez-Palencia

include/net/pkt_sched.h

@@ -155,4 +155,9 @@ struct tc_cbs_qopt_offload {
 	s32 sendslope;
 };
 
+struct tc_etf_qopt_offload {
+	u8 enable;
+	s32 queue;
+};
+
 #endif

include/uapi/linux/pkt_sched.h

@@ -944,6 +944,7 @@ struct tc_etf_qopt {
 	__s32 clockid;
 	__u32 flags;
 #define TC_ETF_DEADLINE_MODE_ON	BIT(0)
+#define TC_ETF_OFFLOAD_ON	BIT(1)
 };
 
 enum {

net/sched/sch_etf.c

@@ -20,8 +20,10 @@
 #include <net/sock.h>
 
 #define DEADLINE_MODE_IS_ON(x) ((x)->flags & TC_ETF_DEADLINE_MODE_ON)
+#define OFFLOAD_IS_ON(x) ((x)->flags & TC_ETF_OFFLOAD_ON)
 
 struct etf_sched_data {
+	bool offload;
 	bool deadline_mode;
 	int clockid;
 	int queue;
@@ -45,6 +47,9 @@ static inline int validate_input_params(struct tc_etf_qopt *qopt,
 	 *	* Dynamic clockids are not supported.
 	 *
 	 *	* Delta must be a positive integer.
+	 *
+	 * Also note that for the HW offload case, we must
+	 * expect that system clocks have been synchronized to PHC.
 	 */
 	if (qopt->clockid < 0) {
 		NL_SET_ERR_MSG(extack, "Dynamic clockids are not supported");
@@ -225,6 +230,56 @@ static struct sk_buff *etf_dequeue_timesortedlist(struct Qdisc *sch)
 	return skb;
 }
 
+static void etf_disable_offload(struct net_device *dev,
+				struct etf_sched_data *q)
+{
+	struct tc_etf_qopt_offload etf = { };
+	const struct net_device_ops *ops;
+	int err;
+
+	if (!q->offload)
+		return;
+
+	ops = dev->netdev_ops;
+	if (!ops->ndo_setup_tc)
+		return;
+
+	etf.queue = q->queue;
+	etf.enable = 0;
+
+	err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_ETF, &etf);
+	if (err < 0)
+		pr_warn("Couldn't disable ETF offload for queue %d\n",
+			etf.queue);
+}
+
+static int etf_enable_offload(struct net_device *dev, struct etf_sched_data *q,
+			      struct netlink_ext_ack *extack)
+{
+	const struct net_device_ops *ops = dev->netdev_ops;
+	struct tc_etf_qopt_offload etf = { };
+	int err;
+
+	if (q->offload)
+		return 0;
+
+	if (!ops->ndo_setup_tc) {
+		NL_SET_ERR_MSG(extack, "Specified device does not support ETF offload");
+		return -EOPNOTSUPP;
+	}
+
+	etf.queue = q->queue;
+	etf.enable = 1;
+
+	err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_ETF, &etf);
+	if (err < 0) {
+		NL_SET_ERR_MSG(extack, "Specified device failed to setup ETF hardware offload");
+		return err;
+	}
+
+	return 0;
+}
+
 static int etf_init(struct Qdisc *sch, struct nlattr *opt,
 		    struct netlink_ext_ack *extack)
 {
@@ -251,8 +306,9 @@ static int etf_init(struct Qdisc *sch, struct nlattr *opt,
 
 	qopt = nla_data(tb[TCA_ETF_PARMS]);
 
-	pr_debug("delta %d clockid %d deadline %s\n",
+	pr_debug("delta %d clockid %d offload %s deadline %s\n",
 		 qopt->delta, qopt->clockid,
+		 OFFLOAD_IS_ON(qopt) ? "on" : "off",
 		 DEADLINE_MODE_IS_ON(qopt) ? "on" : "off");
 
 	err = validate_input_params(qopt, extack);
@@ -261,9 +317,16 @@ static int etf_init(struct Qdisc *sch, struct nlattr *opt,
 
 	q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
 
+	if (OFFLOAD_IS_ON(qopt)) {
+		err = etf_enable_offload(dev, q, extack);
+		if (err < 0)
+			return err;
+	}
+
 	/* Everything went OK, save the parameters used. */
 	q->delta = qopt->delta;
 	q->clockid = qopt->clockid;
+	q->offload = OFFLOAD_IS_ON(qopt);
 	q->deadline_mode = DEADLINE_MODE_IS_ON(qopt);
 
 	switch (q->clockid) {
@@ -326,10 +389,13 @@ static void etf_reset(struct Qdisc *sch)
 static void etf_destroy(struct Qdisc *sch)
 {
 	struct etf_sched_data *q = qdisc_priv(sch);
+	struct net_device *dev = qdisc_dev(sch);
 
 	/* Only cancel watchdog if it's been initialized. */
 	if (q->watchdog.qdisc == sch)
 		qdisc_watchdog_cancel(&q->watchdog);
+
+	etf_disable_offload(dev, q);
 }
 
 static int etf_dump(struct Qdisc *sch, struct sk_buff *skb)
@@ -344,6 +410,9 @@ static int etf_dump(struct Qdisc *sch, struct sk_buff *skb)
 
 	opt.delta = q->delta;
 	opt.clockid = q->clockid;
+	if (q->offload)
+		opt.flags |= TC_ETF_OFFLOAD_ON;
+
 	if (q->deadline_mode)
 		opt.flags |= TC_ETF_DEADLINE_MODE_ON;