Defer fallback DNS initialization for literal targets (#949)

* Initialize the fallback DNS resolver only when needed * Record lazy DNS startup benchmark results * docs(perf): remeasure lazy DNS against merged Tokio master * docs(perf): verify lazy DNS on current master
2026-11-07 09:46:04 -10:00 · 2026-10-02 20:45:12 +09:00
1 parent 67c08a3310
commit 32d7d2cb17
@@ -0,0 +1,151 @@
+{
+  "metadata": {
+    "base": "67c08a33100362c54b56fde784b0fd234f70fa11",
+    "candidate": "a05592a8a88b77ad85d961137943dfadfe98b612",
+    "environment": "Linux-7.2.6-1-cachyos-x86_64-with-glibc2.44",
+    "rust": "rustc 1.98.1 (48a229cea 2026-09-01) (Arch Linux rust 1:1.98.1-1.1)",
+    "hosts_bytes": 2760051,
+    "profile": "release with LTO",
+    "network_namespace": "unshare --user --map-root-user --net",
+    "common_args": [
+      "--no-config",
+      "--config-path",
+      "/dev/null",
+      "--no-banner",
+      "--scripts",
+      "none",
+      "--greppable",
+      "--ports",
+      "80",
+      "--exclude-ports",
+      "80"
+    ],
+    "workloads": {
+      "literal-ipv4": [
+        "-a",
+        "127.0.0.1"
+      ],
+      "mixed-cidrs": [
+        "-a",
+        "127.0.0.1,192.0.2.0/30,2001:db8::/126",
+        "--exclude-addresses",
+        "192.0.2.1,2001:db8::1"
+      ]
+    },
+    "warmups_each": 2,
+    "samples_each": 20,
+    "binary_cpus": "0-3",
+    "harness_cpus": "8-9",
+    "binary_sha256": {
+      "base": "4d6b090218ff36249ed95f14ec1a82626e8ea33854f3823f19a6de247b1524b8",
+      "dns": "a9d6bf949f56c53d18cc85bc9b53b21bd85a63bcdd04ad78992d392c675c77ac"
+    }
+  },
+  "summary": {
+    "literal-ipv4": {
+      "base_ms": 168.23068849999999,
+      "dns_ms": 2.248762,
+      "samples_each": 20
+    },
+    "mixed-cidrs": {
+      "base_ms": 178.0855925,
+      "dns_ms": 2.4539600000000004,
+      "samples_each": 20
+    }
+  },
+  "samples": {
+    "literal-ipv4": {
+      "base": [
+        143.391226,
+        146.562804,
+        149.615525,
+        151.188597,
+        152.269193,
+        159.499601,
+        164.926958,
+        164.347529,
+        167.208931,
+        165.433184,
+        172.246939,
+        169.252446,
+        172.777899,
+        170.729249,
+        170.092681,
+        171.863255,
+        169.612842,
+        170.857396,
+        173.117403,
+        175.206345
+      ],
+      "dns": [
+        2.241793,
+        1.817341,
+        2.39956,
+        2.048986,
+        3.123401,
+        1.820017,
+        3.615094,
+        2.165312,
+        2.675535,
+        2.103261,
+        2.531392,
+        2.215141,
+        2.572939,
+        2.063803,
+        2.671431,
+        2.059846,
+        2.598858,
+        2.230916,
+        2.678259,
+        2.255731
+      ]
+    },
+    "mixed-cidrs": {
+      "base": [
+        175.504767,
+        178.797842,
+        186.183728,
+        176.885958,
+        177.989816,
+        180.028568,
+        177.66299,
+        174.757221,
+        175.468485,
+        175.328023,
+        177.639639,
+        175.637593,
+        177.922435,
+        185.394396,
+        182.587204,
+        180.58311,
+        178.961137,
+        178.293186,
+        180.482419,
+        178.181369
+      ],
+      "dns": [
+        3.275193,
+        2.114074,
+        2.700771,
+        2.183317,
+        2.606538,
+        2.368046,
+        2.599702,
+        2.238105,
+        2.683892,
+        2.292249,
+        2.528366,
+        2.114478,
+        2.668921,
+        2.103271,
+        3.275514,
+        2.27974,
+        3.103311,
+        2.265298,
+        2.580743,
+        2.379554
+      ]
+    }
+  },
+  "invocations": 88
+}
@@ -0,0 +1,48 @@
+# Lazy DNS initialization benchmark
+
+Compared current Tokio master `67c08a33100362c54b56fde784b0fd234f70fa11` with the lazy-resolver implementation
+at `a05592a8a88b77ad85d961137943dfadfe98b612` on 2026-10-02.
+
+## Method
+
+Both binaries are release builds with LTO, using Rust 1.98.1 on an Intel Core
+Ultra 7 165U running Linux 7.2.6-1-cachyos. Each workload used twenty measured
+runs and two warmups per binary, alternating A/B and B/A order. Binaries used
+CPUs 0-3; the harness used CPUs 8-9. No builds ran during measurement.
+
+The harness ran in a private network namespace. Every invocation excluded
+its only requested port, so no scan traffic was sent. Configuration and
+scripts were disabled. Timing spans process launch through exit, including
+the same `taskset` affinity launcher for both builds.
+
+Common arguments:
+
+```sh
+--no-config --config-path /dev/null --no-banner --scripts none --greppable \
+  --ports 80 --exclude-ports 80
+```
+
+The literal case adds `-a 127.0.0.1`. The mixed case adds
+`-a 127.0.0.1,192.0.2.0/30,2001:db8::/126` and
+`--exclude-addresses 192.0.2.1,2001:db8::1`. Both use `RUST_LOG=rustscan=info`.
+
+## Results
+
+| Workload | Master median | Lazy DNS median | Time saved |
+| --- | ---: | ---: | ---: |
+| Literal IPv4 | 168.23 ms | 2.25 ms | 165.98 ms (98.66%) |
+| IPv4/IPv6 CIDRs and exclusions | 178.09 ms | 2.45 ms | 175.63 ms (98.62%) |
+
+All 88 invocations exited successfully with the expected empty scan output.
+A separate syscall trace of the optimized literal-IP invocation recorded no
+reads of `/etc/hosts` or `/etc/resolv.conf` and no network connects or sends.
+
+This host has a 2,760,051-byte hosts file. Eager Hickory initialization parses
+that file even for numeric targets. Systems with smaller hosts files will
+save less; this measures CLI startup, not socket throughput. Hostnames that
+need fallback DNS still pay resolver initialization once, and parsing order,
+file handling, deduplication and exclusions keep their existing behavior.
+
+[Raw samples, setup and binary hashes](lazy-dns-benchmark-results.json) are
+included. Network-free regression tests verify that literal IPv4/IPv6 targets,
+CIDRs, exclusions, duplicates and empty inputs do not construct the resolver.