[PATCH net-next 7/9] rxrpc: Obtain RTT data by requesting ACKs on DATA packets

David Howells
2016-09-22T00:47:56Z

In addition to sending a PING ACK to gain RTT data, we can set the
RXRPC_REQUEST_ACK flag on a DATA packet and get a REQUESTED-ACK ACK. The
ACK packet contains the serial number of the packet it is in response to,
so we can look through the Tx buffer for a matching DATA packet.

This requires that the data packets be stamped with the time of
transmission as a ktime rather than having the resend_at time in jiffies.

This further requires the resend code to do the resend determination in
ktimes and convert to jiffies to set the timer.

Signed-off-by: David Howells <dhowells@redhat.com>
---

net/rxrpc/ar-internal.h | 7 +++----
net/rxrpc/call_event.c | 20 ++++++++++----------
net/rxrpc/input.c | 35 +++++++++++++++++++++++++++++++++++
net/rxrpc/misc.c | 6 ++++--
net/rxrpc/output.c | 7 +++++--
net/rxrpc/sendmsg.c | 1 -
net/rxrpc/sysctl.c | 2 +-
7 files changed, 58 insertions(+), 20 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 8b47f468eb9d..1c4597b2c6cd 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -142,10 +142,7 @@ struct rxrpc_host_header {
*/
struct rxrpc_skb_priv {
union {
- unsigned long resend_at; /* time in jiffies at which to resend */
- struct {
- u8 nr_jumbo; /* Number of jumbo subpackets */
- };
+ u8 nr_jumbo; /* Number of jumbo subpackets */
};
union {
unsigned int offset; /* offset into buffer of next read */
@@ -663,6 +660,7 @@ extern const char rxrpc_recvmsg_traces[rxrpc_recvmsg__nr_trace][5];

enum rxrpc_rtt_tx_trace {
rxrpc_rtt_tx_ping,
+ rxrpc_rtt_tx_data,
rxrpc_rtt_tx__nr_trace
};

@@ -670,6 +668,7 @@ extern const char rxrpc_rtt_tx_traces[rxrpc_rtt_tx__nr_trace][5];

enum rxrpc_rtt_rx_trace {
rxrpc_rtt_rx_ping_response,
+ rxrpc_rtt_rx_requested_ack,
rxrpc_rtt_rx__nr_trace
};

diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 34ad967f2d81..77802da14456 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -142,12 +142,14 @@ static void rxrpc_resend(struct rxrpc_call *call)
struct rxrpc_skb_priv *sp;
struct sk_buff *skb;
rxrpc_seq_t cursor, seq, top;
- unsigned long resend_at, now;
+ ktime_t now = ktime_get_real(), max_age, oldest, resend_at;
int ix;
u8 annotation, anno_type;

_enter("{%d,%d}", call->tx_hard_ack, call->tx_top);

+ max_age = ktime_sub_ms(now, rxrpc_resend_timeout);
+
spin_lock_bh(&call->lock);

cursor = call->tx_hard_ack;
@@ -160,8 +162,7 @@ static void rxrpc_resend(struct rxrpc_call *call)
* the packets in the Tx buffer we're going to resend and what the new
* resend timeout will be.
*/
- now = jiffies;
- resend_at = now + rxrpc_resend_timeout;
+ oldest = now;
for (seq = cursor + 1; before_eq(seq, top); seq++) {
ix = seq & RXRPC_RXTX_BUFF_MASK;
annotation = call->rxtx_annotations[ix];
@@ -175,9 +176,9 @@ static void rxrpc_resend(struct rxrpc_call *call)
sp = rxrpc_skb(skb);

if (anno_type == RXRPC_TX_ANNO_UNACK) {
- if (time_after(sp->resend_at, now)) {
- if (time_before(sp->resend_at, resend_at))
- resend_at = sp->resend_at;
+ if (ktime_after(skb->tstamp, max_age)) {
+ if (ktime_before(skb->tstamp, oldest))
+ oldest = skb->tstamp;
continue;
}
}
@@ -186,7 +187,9 @@ static void rxrpc_resend(struct rxrpc_call *call)
call->rxtx_annotations[ix] = RXRPC_TX_ANNO_RETRANS | annotation;
}

- call->resend_at = resend_at;
+ resend_at = ktime_sub(ktime_add_ns(oldest, rxrpc_resend_timeout), now);
+ call->resend_at = jiffies +
+ usecs_to_jiffies(ktime_to_ns(resend_at) / NSEC_PER_USEC);

/* Now go through the Tx window and perform the retransmissions. We
* have to drop the lock for each send. If an ACK comes in whilst the
@@ -205,15 +208,12 @@ static void rxrpc_resend(struct rxrpc_call *call)
spin_unlock_bh(&call->lock);

if (rxrpc_send_data_packet(call, skb) < 0) {
- call->resend_at = now + 2;
rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
return;
}

if (rxrpc_is_client_call(call))
rxrpc_expose_client_call(call);
- sp = rxrpc_skb(skb);
- sp->resend_at = now + rxrpc_resend_timeout;

rxrpc_free_skb(skb, rxrpc_skb_tx_freed);
spin_lock_bh(&call->lock);
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index a0a5bd108c9e..c121949de3c8 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -356,6 +356,38 @@ ack:
}

/*
+ * Process a requested ACK.
+ */
+static void rxrpc_input_requested_ack(struct rxrpc_call *call,
+ ktime_t resp_time,
+ rxrpc_serial_t orig_serial,
+ rxrpc_serial_t ack_serial)
+{
+ struct rxrpc_skb_priv *sp;
+ struct sk_buff *skb;
+ ktime_t sent_at;
+ int ix;
+
+ for (ix = 0; ix < RXRPC_RXTX_BUFF_SIZE; ix++) {
+ skb = call->rxtx_buffer[ix];
+ if (!skb)
+ continue;
+
+ sp = rxrpc_skb(skb);
+ if (sp->hdr.serial != orig_serial)
+ continue;
+ smp_rmb();
+ sent_at = skb->tstamp;
+ goto found;
+ }
+ return;
+
+found:
+ rxrpc_peer_add_rtt(call, rxrpc_rtt_rx_requested_ack,
+ orig_serial, ack_serial, sent_at, resp_time);
+}
+
+/*
* Process a ping response.
*/
static void rxrpc_input_ping_response(struct rxrpc_call *call,
@@ -508,6 +540,9 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
if (buf.ack.reason == RXRPC_ACK_PING_RESPONSE)
rxrpc_input_ping_response(call, skb->tstamp, acked_serial,
sp->hdr.serial);
+ if (buf.ack.reason == RXRPC_ACK_REQUESTED)
+ rxrpc_input_requested_ack(call, skb->tstamp, acked_serial,
+ sp->hdr.serial);

if (buf.ack.reason == RXRPC_ACK_PING) {
_proto("Rx ACK %%%u PING Request", sp->hdr.serial);
diff --git a/net/rxrpc/misc.c b/net/rxrpc/misc.c
index 56e668352fc7..0d425e707f22 100644
--- a/net/rxrpc/misc.c
+++ b/net/rxrpc/misc.c
@@ -68,9 +68,9 @@ unsigned int rxrpc_rx_mtu = 5692;
unsigned int rxrpc_rx_jumbo_max = 4;

/*
- * Time till packet resend (in jiffies).
+ * Time till packet resend (in milliseconds).
*/
-unsigned int rxrpc_resend_timeout = 4 * HZ;
+unsigned int rxrpc_resend_timeout = 4 * 1000;

const char *const rxrpc_pkts[] = {
"?00",
@@ -186,8 +186,10 @@ const char rxrpc_recvmsg_traces[rxrpc_recvmsg__nr_trace][5] = {

const char rxrpc_rtt_tx_traces[rxrpc_rtt_tx__nr_trace][5] = {
[rxrpc_rtt_tx_ping] = "PING",
+ [rxrpc_rtt_tx_data] = "DATA",
};

const char rxrpc_rtt_rx_traces[rxrpc_rtt_rx__nr_trace][5] = {
[rxrpc_rtt_rx_ping_response] = "PONG",
+ [rxrpc_rtt_rx_requested_ack] = "RACK",
};
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 0d89cd3f2c01..db01fbb70d23 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -300,9 +300,12 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb)
goto send_fragmentable;

done:
- if (ret == 0) {
- sp->resend_at = jiffies + rxrpc_resend_timeout;
+ if (ret >= 0) {
+ skb->tstamp = ktime_get_real();
+ smp_wmb();
sp->hdr.serial = serial;
+ if (whdr.flags & RXRPC_REQUEST_ACK)
+ trace_rxrpc_rtt_tx(call, rxrpc_rtt_tx_data, serial);
}
_leave(" = %d [%u]", ret, call->peer->maxdata);
return ret;
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index 3c969de3ef05..607223f4f871 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -137,7 +137,6 @@ static void rxrpc_queue_packet(struct rxrpc_call *call, struct sk_buff *skb,
if (seq == 1 && rxrpc_is_client_call(call))
rxrpc_expose_client_call(call);

- sp->resend_at = jiffies + rxrpc_resend_timeout;
ret = rxrpc_send_data_packet(call, skb);
if (ret < 0) {
_debug("need instant resend %d", ret);
diff --git a/net/rxrpc/sysctl.c b/net/rxrpc/sysctl.c
index a03c61c672f5..13d1df03ebac 100644
--- a/net/rxrpc/sysctl.c
+++ b/net/rxrpc/sysctl.c
@@ -59,7 +59,7 @@ static struct ctl_table rxrpc_sysctl_table[] = {
.data = &rxrpc_resend_timeout,
.maxlen = sizeof(unsigned int),
.mode = 0644,
- .proc_handler = proc_dointvec_ms_jiffies,
+ .proc_handler = proc_dointvec,
.extra1 = (void *)&one,
},
{