[PATCH mptcp-next v3 14/15] selftests/bpf: Add bpf_burst scheduler

[Geliang Tang <geliang.tang@suse.com>]

This patch implements the burst BPF MPTCP scheduler, named bpf_burst,
which is the default scheduler in protocol.c.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |   3 +
 .../selftests/bpf/progs/mptcp_bpf_burst.c     | 195 ++++++++++++++++++
 2 files changed, 198 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/mptcp_bpf_burst.c

diff --git a/tools/testing/selftests/bpf/bpf_tcp_helpers.h b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
index dddb51a47740..d42a0c00ed73 100644
--- a/tools/testing/selftests/bpf/bpf_tcp_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_tcp_helpers.h
@@ -234,12 +234,15 @@ extern void tcp_cong_avoid_ai(struct tcp_sock *tp, __u32 w, __u32 acked) __ksym;
 #define MPTCP_SUBFLOWS_MAX	8
 
 struct mptcp_subflow_context {
+	unsigned long avg_pacing_rate;
 	__u32	backup : 1;
+	__u8	stale_count;
 	struct	sock *tcp_sock;	    /* tcp sk backpointer */
 } __attribute__((preserve_access_index));
 
 struct mptcp_sched_data {
 	struct sock	*last_snd;
+	int		snd_burst;
 	bool		reinject;
 	struct mptcp_subflow_context *contexts[MPTCP_SUBFLOWS_MAX];
 } __attribute__((preserve_access_index));
diff --git a/tools/testing/selftests/bpf/progs/mptcp_bpf_burst.c b/tools/testing/selftests/bpf/progs/mptcp_bpf_burst.c
new file mode 100644
index 000000000000..305829162ce5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcp_bpf_burst.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023, SUSE. */
+
+#include <linux/bpf.h>
+#include <limits.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct subflow_send_info {
+	struct sock *ssk;
+	__u64 linger_time;
+};
+
+static inline struct sock *
+mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
+{
+	return subflow->tcp_sock;
+}
+
+extern bool mptcp_subflow_active(struct mptcp_subflow_context *subflow) __ksym;
+extern long mptcp_timeout_from_subflow(const struct mptcp_subflow_context *subflow) __ksym;
+extern void mptcp_set_timer(struct sock *sk, long tout) __ksym;
+extern bool mptcp_stream_memory_free(struct mptcp_subflow_context *subflow) __ksym;
+extern __u64 mptcp_get_linger_time(struct sock *ssk, __u32 pace) __ksym;
+extern __u32 mptcp_get_burst(const struct mptcp_sock *msk) __ksym;
+extern unsigned long mptcp_get_pacing_rate(struct mptcp_subflow_context *subflow, __u32 burst) __ksym;
+extern bool mptcp_rtx_and_write_queues_empty(const struct sock *sk) __ksym;
+extern void mptcp_pm_subflow_chk_stale(const struct mptcp_sock *msk, struct sock *ssk) __ksym;
+
+#define SSK_MODE_ACTIVE	0
+#define SSK_MODE_BACKUP	1
+#define SSK_MODE_MAX	2
+
+SEC("struct_ops/mptcp_sched_burst_init")
+void BPF_PROG(mptcp_sched_burst_init, const struct mptcp_sock *msk)
+{
+}
+
+SEC("struct_ops/mptcp_sched_burst_release")
+void BPF_PROG(mptcp_sched_burst_release, const struct mptcp_sock *msk)
+{
+}
+
+void BPF_STRUCT_OPS(bpf_burst_data_init, const struct mptcp_sock *msk,
+		    struct mptcp_sched_data *data)
+{
+	mptcp_sched_data_set_contexts(msk, data);
+}
+
+static int bpf_burst_get_send(const struct mptcp_sock *msk,
+			      struct mptcp_sched_data *data)
+{
+	struct subflow_send_info send_info[SSK_MODE_MAX];
+	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	int i, nr_active = 0;
+	__u32 pace, burst;
+	__u64 linger_time;
+	struct sock *ssk;
+	long tout = 0;
+	int nr = 0;
+
+	/* pick the subflow with the lower wmem/wspace ratio */
+	for (i = 0; i < SSK_MODE_MAX; ++i) {
+		send_info[i].ssk = NULL;
+		send_info[i].linger_time = -1;
+	}
+
+	for (i = 0; i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (!data->contexts[i])
+			break;
+
+		subflow = data->contexts[i];
+		ssk = mptcp_subflow_tcp_sock(subflow);
+		if (!mptcp_subflow_active(subflow))
+			continue;
+
+		tout = max(tout, mptcp_timeout_from_subflow(subflow));
+		nr_active += !subflow->backup;
+		pace = subflow->avg_pacing_rate;
+		if (!pace) {
+			/* init pacing rate from socket */
+			subflow->avg_pacing_rate = ssk->sk_pacing_rate;
+			pace = subflow->avg_pacing_rate;
+			if (!pace)
+				continue;
+		}
+
+		linger_time = mptcp_get_linger_time(ssk, pace);
+		if (linger_time < send_info[subflow->backup].linger_time) {
+			send_info[subflow->backup].ssk = ssk;
+			send_info[subflow->backup].linger_time = linger_time;
+		}
+	}
+	mptcp_set_timer(sk, tout);
+
+	/* pick the best backup if no other subflow is active */
+	if (!nr_active)
+		send_info[SSK_MODE_ACTIVE].ssk = send_info[SSK_MODE_BACKUP].ssk;
+
+	ssk = send_info[SSK_MODE_ACTIVE].ssk;
+	if (!ssk)
+		return -1;
+
+	for (i = 0; i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (data->contexts[i]->tcp_sock == ssk) {
+			nr = i;
+			break;
+		}
+	}
+	subflow = data->contexts[nr];
+
+	if (!mptcp_stream_memory_free(subflow))
+		return -1;
+
+	burst = mptcp_get_burst(msk);
+	if (!burst)
+		goto out;
+
+	data->snd_burst = burst;
+	subflow->avg_pacing_rate = mptcp_get_pacing_rate(subflow, burst);
+
+out:
+	mptcp_subflow_set_scheduled(subflow, true);
+	return 0;
+}
+
+static int bpf_burst_get_retrans(const struct mptcp_sock *msk,
+				 struct mptcp_sched_data *data)
+{
+	struct sock *backup = NULL, *pick = NULL, *ret = NULL;
+	struct mptcp_subflow_context *subflow;
+	int min_stale_count = INT_MAX;
+	struct sock *ssk;
+	int i, nr = 0;
+
+	for (i = 0; i < MPTCP_SUBFLOWS_MAX; i++) {
+		if (!data->contexts[i])
+			break;
+
+		subflow = data->contexts[i];
+		ssk = mptcp_subflow_tcp_sock(subflow);
+		if (!mptcp_subflow_active(subflow))
+			continue;
+
+		/* still data outstanding at TCP level? skip this */
+		if (!mptcp_rtx_and_write_queues_empty(ssk)) {
+			mptcp_pm_subflow_chk_stale(msk, ssk);
+			min_stale_count = min(min_stale_count, subflow->stale_count);
+			continue;
+		}
+
+		if (subflow->backup) {
+			if (!backup)
+				backup = ssk;
+			continue;
+		}
+
+		if (!pick)
+			pick = ssk;
+	}
+
+	if (pick)
+		ret = pick;
+	ret = min_stale_count > 1 ? backup : NULL;
+
+	if (ret) {
+		for (i = 0; i < MPTCP_SUBFLOWS_MAX; i++) {
+			if (data->contexts[i]->tcp_sock == ret) {
+				nr = i;
+				break;
+			}
+		}
+	}
+	mptcp_subflow_set_scheduled(data->contexts[nr], true);
+	return 0;
+}
+
+int BPF_STRUCT_OPS(bpf_burst_get_subflow, const struct mptcp_sock *msk,
+		   struct mptcp_sched_data *data)
+{
+	if (data->reinject)
+		return bpf_burst_get_retrans(msk, data);
+	return bpf_burst_get_send(msk, data);
+}
+
+SEC(".struct_ops")
+struct mptcp_sched_ops burst = {
+	.init		= (void *)mptcp_sched_burst_init,
+	.release	= (void *)mptcp_sched_burst_release,
+	.data_init	= (void *)bpf_burst_data_init,
+	.get_subflow	= (void *)bpf_burst_get_subflow,
+	.name		= "bpf_burst",
+};
-- 
2.35.3