rxrpc: Obtain RTT data by requesting ACKs on DATA packets

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>

7 files changed, 57 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..adb2ec61e21f 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 +187,8 @@ 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 + nsecs_to_jiffies(ktime_to_ns(resend_at));
 
         /* 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 +207,12 @@ 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,
         },
         {