rxrpc: Add per-peer RTT tracker
Add a function to track the average RTT for a peer. Sources of RTT data
will be added in subsequent patches.
The RTT data will be useful in the future for determining resend timeouts
and for handling the slow-start part of the Rx protocol.
Also add a pair of tracepoints, one to log transmissions to elicit a
response for RTT purposes and one to log responses that contribute RTT
data.
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/net/rxrpc/peer_event.c b/net/rxrpc/peer_event.c
index 18276e7..bf13b84 100644
--- a/net/rxrpc/peer_event.c
+++ b/net/rxrpc/peer_event.c
@@ -305,3 +305,44 @@
rxrpc_put_peer(peer);
_leave("");
}
+
+/*
+ * Add RTT information to cache. This is called in softirq mode and has
+ * exclusive access to the peer RTT data.
+ */
+void rxrpc_peer_add_rtt(struct rxrpc_call *call, enum rxrpc_rtt_rx_trace why,
+ rxrpc_serial_t send_serial, rxrpc_serial_t resp_serial,
+ ktime_t send_time, ktime_t resp_time)
+{
+ struct rxrpc_peer *peer = call->peer;
+ s64 rtt;
+ u64 sum = peer->rtt_sum, avg;
+ u8 cursor = peer->rtt_cursor, usage = peer->rtt_usage;
+
+ rtt = ktime_to_ns(ktime_sub(resp_time, send_time));
+ if (rtt < 0)
+ return;
+
+ /* Replace the oldest datum in the RTT buffer */
+ sum -= peer->rtt_cache[cursor];
+ sum += rtt;
+ peer->rtt_cache[cursor] = rtt;
+ peer->rtt_cursor = (cursor + 1) & (RXRPC_RTT_CACHE_SIZE - 1);
+ peer->rtt_sum = sum;
+ if (usage < RXRPC_RTT_CACHE_SIZE) {
+ usage++;
+ peer->rtt_usage = usage;
+ }
+
+ /* Now recalculate the average */
+ if (usage == RXRPC_RTT_CACHE_SIZE) {
+ avg = sum / RXRPC_RTT_CACHE_SIZE;
+ } else {
+ avg = sum;
+ do_div(avg, usage);
+ }
+
+ peer->rtt = avg;
+ trace_rxrpc_rtt_rx(call, why, send_serial, resp_serial, rtt,
+ usage, avg);
+}