sunvnet: Avoid sending superfluous LDC messages.
When sending out a burst of packets across multiple descriptors,
it is sufficient to send one LDC "start" trigger for
the first descriptor, so do not send an LDC "start" for every
pass through vnet_start_xmit. Similarly, it is sufficient to send
one "DRING_STOPPED" trigger for the last dring (and if that
fails, hold off and send the trigger later).
Optimizations to the number of LDC messages helps avoid
filling up the LDC channel with superfluous LDC messages
that risk triggering flow-control on the channel,
and also boosts performance.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Raghuram Kothakota <raghuram.kothakota@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/sun/sunvnet.c b/drivers/net/ethernet/sun/sunvnet.c
index a4657a4..763cdfc 100644
--- a/drivers/net/ethernet/sun/sunvnet.c
+++ b/drivers/net/ethernet/sun/sunvnet.c
@@ -37,6 +37,8 @@
*/
#define VNET_MAX_RETRIES 10
+static int __vnet_tx_trigger(struct vnet_port *port, u32 start);
+
/* Ordered from largest major to lowest */
static struct vio_version vnet_versions[] = {
{ .major = 1, .minor = 0 },
@@ -283,10 +285,18 @@
port->raddr[0], port->raddr[1],
port->raddr[2], port->raddr[3],
port->raddr[4], port->raddr[5]);
- err = -ECONNRESET;
+ break;
}
} while (err == -EAGAIN);
+ if (err <= 0 && vio_dring_state == VIO_DRING_STOPPED) {
+ port->stop_rx_idx = end;
+ port->stop_rx = true;
+ } else {
+ port->stop_rx_idx = 0;
+ port->stop_rx = false;
+ }
+
return err;
}
@@ -448,7 +458,7 @@
struct net_device *dev;
struct vnet *vp;
u32 end;
-
+ struct vio_net_desc *desc;
if (unlikely(pkt->tag.stype_env != VIO_DRING_DATA))
return 0;
@@ -456,7 +466,24 @@
if (unlikely(!idx_is_pending(dr, end)))
return 0;
+ /* sync for race conditions with vnet_start_xmit() and tell xmit it
+ * is time to send a trigger.
+ */
dr->cons = next_idx(end, dr);
+ desc = vio_dring_entry(dr, dr->cons);
+ if (desc->hdr.state == VIO_DESC_READY && port->start_cons) {
+ /* vnet_start_xmit() just populated this dring but missed
+ * sending the "start" LDC message to the consumer.
+ * Send a "start" trigger on its behalf.
+ */
+ if (__vnet_tx_trigger(port, dr->cons) > 0)
+ port->start_cons = false;
+ else
+ port->start_cons = true;
+ } else {
+ port->start_cons = true;
+ }
+
vp = port->vp;
dev = vp->dev;
@@ -597,7 +624,7 @@
local_irq_restore(flags);
}
-static int __vnet_tx_trigger(struct vnet_port *port)
+static int __vnet_tx_trigger(struct vnet_port *port, u32 start)
{
struct vio_dring_state *dr = &port->vio.drings[VIO_DRIVER_TX_RING];
struct vio_dring_data hdr = {
@@ -608,12 +635,21 @@
.sid = vio_send_sid(&port->vio),
},
.dring_ident = dr->ident,
- .start_idx = dr->prod,
+ .start_idx = start,
.end_idx = (u32) -1,
};
int err, delay;
int retries = 0;
+ if (port->stop_rx) {
+ err = vnet_send_ack(port,
+ &port->vio.drings[VIO_DRIVER_RX_RING],
+ port->stop_rx_idx, -1,
+ VIO_DRING_STOPPED);
+ if (err <= 0)
+ return err;
+ }
+
hdr.seq = dr->snd_nxt;
delay = 1;
do {
@@ -734,7 +770,30 @@
d->hdr.state = VIO_DESC_READY;
- err = __vnet_tx_trigger(port);
+ /* Exactly one ldc "start" trigger (for dr->cons) needs to be sent
+ * to notify the consumer that some descriptors are READY.
+ * After that "start" trigger, no additional triggers are needed until
+ * a DRING_STOPPED is received from the consumer. The dr->cons field
+ * (set up by vnet_ack()) has the value of the next dring index
+ * that has not yet been ack-ed. We send a "start" trigger here
+ * if, and only if, start_cons is true (reset it afterward). Conversely,
+ * vnet_ack() should check if the dring corresponding to cons
+ * is marked READY, but start_cons was false.
+ * If so, vnet_ack() should send out the missed "start" trigger.
+ *
+ * Note that the wmb() above makes sure the cookies et al. are
+ * not globally visible before the VIO_DESC_READY, and that the
+ * stores are ordered correctly by the compiler. The consumer will
+ * not proceed until the VIO_DESC_READY is visible assuring that
+ * the consumer does not observe anything related to descriptors
+ * out of order. The HV trap from the LDC start trigger is the
+ * producer to consumer announcement that work is available to the
+ * consumer
+ */
+ if (!port->start_cons)
+ goto ldc_start_done; /* previous trigger suffices */
+
+ err = __vnet_tx_trigger(port, dr->cons);
if (unlikely(err < 0)) {
netdev_info(dev, "TX trigger error %d\n", err);
d->hdr.state = VIO_DESC_FREE;
@@ -742,6 +801,9 @@
goto out_dropped_unlock;
}
+ldc_start_done:
+ port->start_cons = false;
+
dev->stats.tx_packets++;
dev->stats.tx_bytes += skb->len;
@@ -1035,6 +1097,7 @@
(sizeof(struct ldc_trans_cookie) * 2));
dr->num_entries = VNET_TX_RING_SIZE;
dr->prod = dr->cons = 0;
+ port->start_cons = true; /* need an initial trigger */
dr->pending = VNET_TX_RING_SIZE;
dr->ncookies = ncookies;
diff --git a/drivers/net/ethernet/sun/sunvnet.h b/drivers/net/ethernet/sun/sunvnet.h
index de5c2c6..da49337 100644
--- a/drivers/net/ethernet/sun/sunvnet.h
+++ b/drivers/net/ethernet/sun/sunvnet.h
@@ -40,6 +40,10 @@
struct vnet_tx_entry tx_bufs[VNET_TX_RING_SIZE];
struct list_head list;
+
+ u32 stop_rx_idx;
+ bool stop_rx;
+ bool start_cons;
};
static inline struct vnet_port *to_vnet_port(struct vio_driver_state *vio)