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Message-ID: <20241028213541.1529-11-ouster@cs.stanford.edu>
Date: Mon, 28 Oct 2024 14:35:37 -0700
From: John Ousterhout <ouster@...stanford.edu>
To: netdev@...r.kernel.org
Cc: John Ousterhout <ouster@...stanford.edu>
Subject: [PATCH net-next 10/12] net: homa: create homa_timer.c
This file contains code that wakes up periodically to check for
missing data, initiate retransmissions, and declare peer nodes
"dead".
Signed-off-by: John Ousterhout <ouster@...stanford.edu>
---
net/homa/homa_timer.c | 158 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 158 insertions(+)
create mode 100644 net/homa/homa_timer.c
diff --git a/net/homa/homa_timer.c b/net/homa/homa_timer.c
new file mode 100644
index 000000000000..bce7c02bb1cd
--- /dev/null
+++ b/net/homa/homa_timer.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+/* This file handles timing-related functions for Homa, such as retries
+ * and timeouts.
+ */
+
+#include "homa_impl.h"
+#include "homa_peer.h"
+#include "homa_rpc.h"
+
+/**
+ * homa_check_rpc() - Invoked for each RPC during each timer pass; does
+ * most of the work of checking for time-related actions such as sending
+ * resends, aborting RPCs for which there is no response, and sending
+ * requests for acks. It is separate from homa_timer because homa_timer
+ * got too long and deeply indented.
+ * @rpc: RPC to check; must be locked by the caller.
+ */
+void homa_check_rpc(struct homa_rpc *rpc)
+{
+ struct homa *homa = rpc->hsk->homa;
+ struct resend_header resend;
+
+ /* See if we need to request an ack for this RPC. */
+ if (!homa_is_client(rpc->id) && rpc->state == RPC_OUTGOING &&
+ rpc->msgout.next_xmit_offset >= rpc->msgout.length) {
+ if (rpc->done_timer_ticks == 0) {
+ rpc->done_timer_ticks = homa->timer_ticks;
+ } else {
+ /* >= comparison that handles tick wrap-around. */
+ if ((rpc->done_timer_ticks + homa->request_ack_ticks
+ - 1 - homa->timer_ticks) & 1 << 31) {
+ struct need_ack_header h;
+
+ homa_xmit_control(NEED_ACK, &h, sizeof(h), rpc);
+ }
+ }
+ }
+
+ if (rpc->state == RPC_INCOMING) {
+ if (rpc->msgin.num_bpages == 0) {
+ /* Waiting for buffer space, so no problem. */
+ rpc->silent_ticks = 0;
+ return;
+ }
+ } else if (!homa_is_client(rpc->id)) {
+ /* We're the server and we've received the input message;
+ * no need to worry about retries.
+ */
+ rpc->silent_ticks = 0;
+ return;
+ }
+
+ if (rpc->state == RPC_OUTGOING) {
+ if (rpc->msgout.next_xmit_offset < rpc->msgout.length) {
+ /* There are bytes that we haven't transmitted,
+ * so no need to be concerned; the ball is in our court.
+ */
+ rpc->silent_ticks = 0;
+ return;
+ }
+ }
+
+ if (rpc->silent_ticks < homa->resend_ticks)
+ return;
+ if (rpc->silent_ticks >= homa->timeout_ticks) {
+ homa_rpc_abort(rpc, -ETIMEDOUT);
+ return;
+ }
+ if (((rpc->silent_ticks - homa->resend_ticks) % homa->resend_interval)
+ != 0)
+ return;
+
+ /* Issue a resend for the bytes just after the last ones received
+ * (gaps in the middle were already handled by homa_gap_retry above).
+ */
+ if (rpc->msgin.length < 0) {
+ /* Haven't received any data for this message; request
+ * retransmission of just the first packet (the sender
+ * will send at least one full packet, regardless of
+ * the length below).
+ */
+ resend.offset = htonl(0);
+ resend.length = htonl(100);
+ } else {
+ homa_gap_retry(rpc);
+ resend.offset = htonl(rpc->msgin.recv_end);
+ resend.length = htonl(rpc->msgin.length - rpc->msgin.recv_end);
+ if (resend.length == 0)
+ return;
+ }
+ homa_xmit_control(RESEND, &resend, sizeof(resend), rpc);
+}
+
+/**
+ * homa_timer() - This function is invoked at regular intervals ("ticks")
+ * to implement retries and aborts for Homa.
+ * @homa: Overall data about the Homa protocol implementation.
+ */
+void homa_timer(struct homa *homa)
+{
+ struct homa_socktab_scan scan;
+ struct homa_sock *hsk;
+ struct homa_rpc *rpc;
+ int total_rpcs = 0;
+ int rpc_count = 0;
+
+ homa->timer_ticks++;
+
+ /* Scan all existing RPCs in all sockets. The rcu_read_lock
+ * below prevents sockets from being deleted during the scan.
+ */
+ rcu_read_lock();
+ for (hsk = homa_socktab_start_scan(homa->port_map, &scan);
+ hsk; hsk = homa_socktab_next(&scan)) {
+ while (hsk->dead_skbs >= homa->dead_buffs_limit)
+ /* If we get here, it means that homa_wait_for_message
+ * isn't keeping up with RPC reaping, so we'll help
+ * out. See reap.txt for more info.
+ */
+ if (homa_rpc_reap(hsk, hsk->homa->reap_limit) == 0)
+ break;
+
+ if (list_empty(&hsk->active_rpcs) || hsk->shutdown)
+ continue;
+
+ if (!homa_protect_rpcs(hsk))
+ continue;
+ list_for_each_entry_rcu(rpc, &hsk->active_rpcs, active_links) {
+ total_rpcs++;
+ homa_rpc_lock(rpc, "homa_timer");
+ if (rpc->state == RPC_IN_SERVICE) {
+ rpc->silent_ticks = 0;
+ homa_rpc_unlock(rpc);
+ continue;
+ }
+ rpc->silent_ticks++;
+ homa_check_rpc(rpc);
+ homa_rpc_unlock(rpc);
+ rpc_count++;
+ if (rpc_count >= 10) {
+ /* Give other kernel threads a chance to run
+ * on this core. Must release the RCU read lock
+ * while doing this.
+ */
+ rcu_read_unlock();
+ schedule();
+ rcu_read_lock();
+ rpc_count = 0;
+ }
+ }
+ homa_unprotect_rpcs(hsk);
+ }
+ rcu_read_unlock();
+
+// if (total_rpcs > 0)
+// tt_record1("homa_timer finished scanning %d RPCs", total_rpcs);
+}
--
2.34.1
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