From: Matt Corallo <git@bluematt.me>
Date: Tue, 6 Apr 2021 14:05:07 +0000 (-0400)
Subject: Less effecient, but much, much less naive rate-limiter
X-Git-Url: http://git.bitcoin.ninja/index.cgi?p=flowspec-xdp;a=commitdiff_plain;h=ce7cb6545f4fd8872f08263733cb2188530e9420

Less effecient, but much, much less naive rate-limiter
---

diff --git a/genrules.py b/genrules.py
index 300900a..a84eacc 100755
--- a/genrules.py
+++ b/genrules.py
@@ -388,19 +388,30 @@ with open("rules.h", "w") as out:
                         mantissa = low_bytes & ((1 << 23) - 1)
                         value = 1.0 + mantissa / (2**23)
                         value *= 2**(exp-127)
-                        first_action = "uint64_t secs = bpf_ktime_get_ns() / 1000000000;\n"
+                        # Note that int64_t will overflow after 292 years of uptime
+                        first_action = "int64_t time = bpf_ktime_get_ns();\n"
                         first_action += f"const uint32_t ratelimitidx = {ratelimitcnt};\n"
+                        first_action += "size_t pktlen = data_end - pktdata;\n"
+                        first_action += "uint64_t extra_bytes = 0;\n"
                         first_action += "struct ratelimit *rate = bpf_map_lookup_elem(&rate_map, &ratelimitidx);\n"
                         first_action += "if (rate) {\n"
                         first_action += "\tbpf_spin_lock(&rate->lock);\n"
-                        first_action += "\tif (secs != rate->bucket_secs) {\n"
-                        first_action += "\t\trate->bucket_secs = secs;\n"
-                        first_action += "\t\trate->bucket_count = 0;\n"
+                        first_action += "\tif (likely(rate->sent_bytes > 0)) {\n"
+                        first_action += "\t\tint64_t diff = time - rate->sent_time;\n"
+                        # Unlikely or not, if the flow is slow, take a perf hit (though with the else if branch it doesn't matter)
+                        first_action += "\t\tif (unlikely(diff > 1000000000))\n"
+                        first_action += "\t\t\trate->sent_bytes = 0;\n"
+                        first_action += "\t\telse if (likely(diff > 0))\n"
+                        first_action += f"\t\t\textra_bytes = ((uint64_t)diff) * {math.floor(value)} / 1000000000;\n"
+                        first_action += "\t}\n"
+                        first_action += "\tif (rate->sent_bytes - ((int64_t)extra_bytes) <= 0) {\n"
+                        first_action += "\t\trate->sent_bytes = data_end - pktdata;\n"
+                        first_action += "\t\trate->sent_time = time;\n"
+                        first_action += "\t\tbpf_spin_unlock(&rate->lock);\n"
+                        first_action += "\t} else {\n"
+                        first_action += "\t\tbpf_spin_unlock(&rate->lock);\n"
+                        first_action += "\t\treturn XDP_DROP;\n"
                         first_action += "\t}\n"
-                        first_action += f"\tif (rate->bucket_count + (data_end - pktdata) > {math.floor(value)})\n"
-                        first_action += "\t\t{ bpf_spin_unlock(&rate->lock); return XDP_DROP; }\n"
-                        first_action += "\trate->bucket_count += data_end - pktdata;\n"
-                        first_action += "\tbpf_spin_unlock(&rate->lock);\n"
                         first_action += "}\n"
                         ratelimitcnt += 1
                 elif ty == "0x8007":
diff --git a/xdp.c b/xdp.c
index d9aa076..8003b89 100644
--- a/xdp.c
+++ b/xdp.c
@@ -165,8 +165,8 @@ struct bpf_map_def SEC("maps") drop_cnt_map = {
 #ifdef RATE_CNT
 struct ratelimit {
 	struct bpf_spin_lock lock;
-	uint64_t bucket_secs;
-	uint64_t bucket_count;
+	int64_t sent_bytes;
+	int64_t sent_time;
 };
 struct {
 	__uint(type, BPF_MAP_TYPE_ARRAY);