[PATCH net-next v18 13/15] net: homa: create homa_timer.c

John Ousterhout
2026-04-10T20:03:42Z

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@cs.stanford.edu>

---
Changes for v14:
* Use new homa_rpc_tx_end function

Changes for v11:
* Cleanup sparse annotations.

Changes for v10:
* Refactor resend mechanism

Changes for v9:
* Reflect changes in socket and peer management
* Minor name changes for clarity

Changes for v7:
* Interface changes to homa_sock_start_scan etc.
* Remove locker argument from locking functions
* Use u64 and __u64 properly
---
net/homa/homa_impl.h | 3 +
net/homa/homa_timer.c | 136 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 139 insertions(+)
create mode 100644 net/homa/homa_timer.c

diff --git a/net/homa/homa_impl.h b/net/homa/homa_impl.h
index b1ca8b25fb9a..4a8df43003de 100644
--- a/net/homa/homa_impl.h
+++ b/net/homa/homa_impl.h
@@ -385,6 +385,9 @@ void homa_resend_pkt(struct sk_buff *skb, struct homa_rpc *rpc,
void homa_rpc_handoff(struct homa_rpc *rpc);
int homa_rpc_tx_end(struct homa_rpc *rpc);
void homa_spin(int ns);
+void homa_timer(struct homa *homa);
+void homa_timer_check_rpc(struct homa_rpc *rpc);
+int homa_timer_main(void *transport);
struct sk_buff *homa_tx_data_pkt_alloc(struct homa_rpc *rpc,
struct iov_iter *iter, int offset,
int length, int max_seg_data);
diff --git a/net/homa/homa_timer.c b/net/homa/homa_timer.c
new file mode 100644
index 000000000000..dcfdcc06c8ab
--- /dev/null
+++ b/net/homa/homa_timer.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: BSD-2-Clause or GPL-2.0+
+
+/* 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"
+#include "homa_stub.h"
+
+/**
+ * homa_timer_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_timer_check_rpc(struct homa_rpc *rpc)
+ __must_hold(rpc->bucket->lock)
+{
+ struct homa *homa = rpc->hsk->homa;
+ int tx_end = homa_rpc_tx_end(rpc);
+
+ /* See if we need to request an ack for this RPC. */
+ if (!homa_is_client(rpc->id) && rpc->state == RPC_OUTGOING &&
+ tx_end == 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 homa_need_ack_hdr 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 (tx_end < rpc->msgout.length) {
+ /* There are granted 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)
+ homa_request_retrans(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 rpc_count = 0;
+
+ homa->timer_ticks++;
+
+ /* Scan all existing RPCs in all sockets. */
+ for (hsk = homa_socktab_start_scan(homa->socktab, &scan);
+ hsk; hsk = homa_socktab_next(&scan)) {
+ while (hsk->dead_skbs >= homa->dead_buffs_limit)
+ /* If we get here, it means that Homa isn't keeping
+ * up with RPC reaping, so we'll help out. See
+ * "RPC Reaping Strategy" in homa_rpc_reap code for
+ * details.
+ */
+ if (homa_rpc_reap(hsk, false) == 0)
+ break;
+
+ if (list_empty(&hsk->active_rpcs) || hsk->shutdown)
+ continue;
+
+ if (!homa_protect_rpcs(hsk))
+ continue;
+ rcu_read_lock();
+ list_for_each_entry_rcu(rpc, &hsk->active_rpcs, active_links) {
+ homa_rpc_lock(rpc);
+ if (rpc->state == RPC_IN_SERVICE) {
+ rpc->silent_ticks = 0;
+ homa_rpc_unlock(rpc);
+ continue;
+ }
+ rpc->silent_ticks++;
+ homa_timer_check_rpc(rpc);
+ homa_rpc_unlock(rpc);
+ rpc_count++;
+ if (rpc_count >= 10) {
+ /* Give other kernel threads a chance to run
+ * on this core.
+ */
+ rcu_read_unlock();
+ schedule();
+ rcu_read_lock();
+ rpc_count = 0;
+ }
+ }
+ rcu_read_unlock();
+ homa_unprotect_rpcs(hsk);
+ }
+ homa_socktab_end_scan(&scan);
+ homa_skb_release_pages(homa);
+ homa_peer_gc(homa->peertab);
+}
--
2.43.0