cnat: maglev fixes & improvements

This fixes the maglev logic which previously
included a wrong simplication.
It moves the maglev logic to its own file,
and adds a test function in the debug cli.

Type: improvement

Change-Id: I2790ae2a26fc1c5739ff02f41d436bfcafd5b380
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>

1 files changed, 375 insertions, 0 deletions

diff --git a/src/plugins/cnat/cnat_maglev.c b/src/plugins/cnat/cnat_maglev.c
new file mode 100644
index 00000000000..669c6479619
--- /dev/null
+++ b/src/plugins/cnat/cnat_maglev.c
@@ -0,0 +1,375 @@
+/* SPDX-License-Identifier: Apache-2.0
+ * Copyright(c) 2022 Cisco Systems, Inc.
+ */
+
+#include <cnat/cnat_maglev.h>
+
+static int
+cnat_maglev_perm_compare (void *_a, void *_b)
+{
+  return *(u64 *) _b - *(u64 *) _a;
+}
+
+/**
+ * Maglev algorithm implementation. This takes permutation as input,
+ * with the values of offset & skip for the backends.
+ * It fills buckets matching the permuntations, provided buckets is
+ * already of length at least M
+ */
+static void
+cnat_maglev_shuffle (cnat_maglev_perm_t *permutation, u32 *buckets)
+{
+  u32 N, M, i, done = 0;
+  u32 *next = 0;
+
+  N = vec_len (permutation);
+  if (N == 0)
+    return;
+
+  M = vec_len (buckets);
+  vec_set (buckets, -1);
+
+  vec_validate (next, N - 1);
+  vec_zero (next);
+
+  while (1)
+    {
+      for (i = 0; i < N; i++)
+	{
+	  u32 c = (permutation[i].offset + next[i] * permutation[i].skip) % M;
+	  while (buckets[c] != (u32) -1)
+	    {
+	      next[i]++;
+	      c = (permutation[i].offset + next[i] * permutation[i].skip) % M;
+	    }
+
+	  buckets[c] = permutation[i].index;
+	  next[i]++;
+	  done++;
+
+	  if (done == M)
+	    {
+	      vec_free (next);
+	      return;
+	    }
+	}
+    }
+}
+
+void
+cnat_translation_init_maglev (cnat_translation_t *ct)
+{
+  cnat_maglev_perm_t *permutations = NULL;
+  cnat_main_t *cm = &cnat_main;
+  cnat_ep_trk_t *trk;
+  u32 backend_index = 0;
+
+  if (vec_len (ct->ct_active_paths) == 0)
+    return;
+
+  vec_foreach (trk, ct->ct_active_paths)
+    {
+      cnat_maglev_perm_t permutation;
+      u32 h1, h2;
+
+      if (AF_IP4 == ip_addr_version (&trk->ct_ep[VLIB_TX].ce_ip))
+	{
+	  u32 a, b, c;
+	  a = ip_addr_v4 (&trk->ct_ep[VLIB_TX].ce_ip).data_u32;
+	  b = (u64) trk->ct_ep[VLIB_TX].ce_port;
+	  c = 0;
+	  hash_v3_mix32 (a, b, c);
+	  hash_v3_finalize32 (a, b, c);
+	  h1 = c;
+	  h2 = b;
+	}
+      else
+	{
+	  u64 a, b, c;
+	  a = ip_addr_v6 (&trk->ct_ep[VLIB_TX].ce_ip).as_u64[0];
+	  b = ip_addr_v6 (&trk->ct_ep[VLIB_TX].ce_ip).as_u64[1];
+	  c = (u64) trk->ct_ep[VLIB_TX].ce_port;
+	  hash_mix64 (a, b, c);
+	  h1 = c;
+	  h2 = b;
+	}
+
+      permutation.offset = h1 % cm->maglev_len;
+      permutation.skip = h2 % (cm->maglev_len - 1) + 1;
+      permutation.index = backend_index++;
+
+      if (trk->ct_flags & CNAT_TRK_FLAG_TEST_DISABLED)
+	continue;
+
+      vec_add1 (permutations, permutation);
+    }
+
+  vec_sort_with_function (permutations, cnat_maglev_perm_compare);
+
+  vec_validate (ct->lb_maglev, cm->maglev_len - 1);
+
+  cnat_maglev_shuffle (permutations, ct->lb_maglev);
+
+  vec_free (permutations);
+}
+
+static int
+cnat_u32_vec_contains (u32 *v, u32 e)
+{
+  int i;
+
+  vec_foreach_index (i, v)
+    if (v[i] == e)
+      return 1;
+
+  return 0;
+}
+
+static void
+cnat_maglev_print_changes (vlib_main_t *vm, u32 *changed_bk_indices,
+			   u32 *old_maglev_lb, u32 *new_maglev_lb)
+{
+  u32 good_flow_buckets = 0, reset_flow_buckets = 0, stable_to_reset = 0;
+  u32 reset_to_stable = 0, switched_stable = 0;
+  for (u32 i = 0; i < vec_len (new_maglev_lb); i++)
+    {
+      u8 is_new_changed =
+	cnat_u32_vec_contains (changed_bk_indices, new_maglev_lb[i]);
+      u8 is_old_changed =
+	cnat_u32_vec_contains (changed_bk_indices, old_maglev_lb[i]);
+      if (new_maglev_lb[i] == old_maglev_lb[i])
+	{
+	  if (is_new_changed)
+	    reset_flow_buckets++;
+	  else
+	    good_flow_buckets++;
+	}
+      else
+	{
+	  if (is_new_changed)
+	    stable_to_reset++;
+	  else if (is_old_changed)
+	    reset_to_stable++;
+	  else
+	    switched_stable++;
+	}
+    }
+  vlib_cli_output (vm,
+		   "good B->B:%d | lost A->A':%d A->B:%d ~%0.2f%% | bad "
+		   "B->A':%d B->C:%d ~%0.2f%%",
+		   good_flow_buckets, reset_flow_buckets, reset_to_stable,
+		   (f64) (reset_flow_buckets + reset_to_stable) /
+		     vec_len (new_maglev_lb) * 100.0,
+		   stable_to_reset, switched_stable,
+		   (f64) (stable_to_reset + switched_stable) /
+		     vec_len (new_maglev_lb) * 100.0);
+}
+
+static u8 *
+format_cnat_maglev_buckets (u8 *s, va_list *args)
+{
+  u32 *buckets = va_arg (*args, u32 *);
+  u32 backend_idx = va_arg (*args, u32);
+  u32 count = va_arg (*args, u32);
+
+  for (u32 ii = 0; ii < vec_len (buckets); ii++)
+    if (buckets[ii] == backend_idx)
+      {
+	s = format (s, "%d,", ii);
+	if (--count == 0)
+	  return (s);
+      }
+  return (s);
+}
+
+static clib_error_t *
+cnat_translation_test_init_maglev (vlib_main_t *vm, unformat_input_t *input,
+				   vlib_cli_command_t *cmd)
+{
+  cnat_translation_t *trs = 0, *ct;
+  u64 num_backends = 0, n_tests = 0;
+  cnat_main_t *cm = &cnat_main;
+  cnat_ep_trk_t *trk;
+  u32 rnd;
+  u32 n_changes = 0, n_remove = 0, verbose = 0;
+
+  while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
+    {
+      if (unformat (input, "tests %d", &n_tests))
+	;
+      else if (unformat (input, "backends %d", &num_backends))
+	;
+      else if (unformat (input, "len %d", &cm->maglev_len))
+	;
+      else if (unformat (input, "change %d", &n_changes))
+	;
+      else if (unformat (input, "rm %d", &n_remove))
+	;
+      else if (unformat (input, "verbose %d", &verbose))
+	;
+      else
+	return (clib_error_return (0, "unknown input '%U'",
+				   format_unformat_error, input));
+    }
+
+  if (num_backends == 0 || n_tests == 0)
+    return (clib_error_return (0, "No backends / tests to run"));
+  ;
+
+  vlib_cli_output (vm, "generating random backends...");
+  rnd = random_default_seed ();
+
+  vec_validate (trs, n_tests - 1);
+  vec_foreach (ct, trs)
+    {
+      vec_validate (ct->ct_active_paths, num_backends - 1);
+      vec_foreach (trk, ct->ct_active_paths)
+	{
+	  trk->ct_flags = 0;
+	  ip_addr_version (&trk->ct_ep[VLIB_TX].ce_ip) = AF_IP4;
+	  ip_addr_v4 (&trk->ct_ep[VLIB_TX].ce_ip).data_u32 = random_u32 (&rnd);
+	  trk->ct_ep[VLIB_TX].ce_port = random_u32 (&rnd);
+	}
+    }
+
+  vlib_cli_output (vm, "testing...");
+  f64 start_time = vlib_time_now (vm);
+  vec_foreach (ct, trs)
+    cnat_translation_init_maglev (ct);
+  f64 d = vlib_time_now (vm) - start_time;
+
+  vlib_cli_output (vm, "Test took : %U", format_duration, d);
+  vlib_cli_output (vm, "Per pool  : %U", format_duration, d / n_tests);
+
+  /* sanity checking of the output */
+  u32 *backend_freqs = 0;
+  vec_validate (backend_freqs, num_backends - 1);
+  vec_foreach (ct, trs)
+    {
+      if (vec_len (ct->lb_maglev) != cm->maglev_len)
+	vlib_cli_output (vm, "Unexpected bucket length %d",
+			 vec_len (ct->lb_maglev));
+
+      vec_zero (backend_freqs);
+      for (u32 i = 0; i < vec_len (ct->lb_maglev); i++)
+	{
+	  if (ct->lb_maglev[i] >= num_backends)
+	    clib_warning ("out of bound backend");
+	  backend_freqs[ct->lb_maglev[i]]++;
+	}
+      u32 fmin = ~0, fmax = 0;
+      for (u32 i = 0; i < num_backends; i++)
+	{
+	  if (backend_freqs[i] > fmax)
+	    fmax = backend_freqs[i];
+	  if (backend_freqs[i] < fmin)
+	    fmin = backend_freqs[i];
+	}
+      f64 fdiff = (fmax - fmin);
+      if (fdiff / vec_len (ct->lb_maglev) - 1 > 0.02)
+	vlib_cli_output (vm, "More than 2%% frequency diff (min %d max %d)",
+			 fmin, fmax);
+    }
+  vec_free (backend_freqs);
+
+  int i = 0;
+  if (verbose)
+    vec_foreach (ct, trs)
+      {
+	vlib_cli_output (vm, "Translation %d", i++);
+	for (u32 i = 0; i < verbose; i++)
+	  {
+	    u32 j = random_u32 (&rnd) % vec_len (ct->ct_active_paths);
+	    trk = &ct->ct_active_paths[j];
+	    vlib_cli_output (
+	      vm, "[%03d] %U:%d buckets:%U", j, format_ip_address,
+	      &trk->ct_ep[VLIB_TX].ce_ip, trk->ct_ep[VLIB_TX].ce_port,
+	      format_cnat_maglev_buckets, ct->lb_maglev, j, verbose);
+	  }
+      }
+
+  if (n_remove != 0)
+    {
+      vlib_cli_output (
+	vm, "Removing %d entries (refered to as A), others (B,C) stay same",
+	n_remove);
+      vec_foreach (ct, trs)
+	{
+	  u32 *old_maglev_lb = 0;
+	  u32 *changed_bk_indices = 0;
+	  if (vec_len (ct->lb_maglev) != cm->maglev_len)
+	    vlib_cli_output (vm, "Unexpected bucket length %d",
+			     vec_len (ct->lb_maglev));
+
+	  vec_validate (changed_bk_indices, n_remove - 1);
+	  for (u32 i = 0; i < n_remove; i++)
+	    {
+	      /* remove n_remove backends from the LB set */
+	      changed_bk_indices[i] =
+		random_u32 (&rnd) % vec_len (ct->ct_active_paths);
+	      trk = &ct->ct_active_paths[changed_bk_indices[i]];
+	      trk->ct_flags |= CNAT_TRK_FLAG_TEST_DISABLED;
+	    }
+
+	  old_maglev_lb = vec_dup (ct->lb_maglev);
+	  cnat_translation_init_maglev (ct);
+
+	  cnat_maglev_print_changes (vm, changed_bk_indices, old_maglev_lb,
+				     ct->lb_maglev);
+
+	  vec_free (changed_bk_indices);
+	  vec_free (old_maglev_lb);
+	}
+    }
+
+  /* Reshuffle and check changes */
+  if (n_changes != 0)
+    {
+      vlib_cli_output (
+	vm,
+	"Changing %d entries (refered to as A->A'), others (B,C) stay same",
+	n_changes);
+      vec_foreach (ct, trs)
+	{
+	  if (vec_len (ct->lb_maglev) != cm->maglev_len)
+	    vlib_cli_output (vm, "Unexpected bucket length %d",
+			     vec_len (ct->lb_maglev));
+
+	  u32 *old_maglev_lb = 0;
+	  u32 *changed_bk_indices = 0;
+
+	  vec_validate (changed_bk_indices, n_changes - 1);
+	  for (u32 i = 0; i < n_changes; i++)
+	    {
+	      /* Change n_changes backends in the LB set */
+	      changed_bk_indices[i] =
+		random_u32 (&rnd) % vec_len (ct->ct_active_paths);
+	      trk = &ct->ct_active_paths[changed_bk_indices[i]];
+	      ip_addr_v4 (&trk->ct_ep[VLIB_TX].ce_ip).data_u32 =
+		random_u32 (&rnd);
+	      trk->ct_ep[VLIB_TX].ce_port = random_u32 (&rnd) & 0xffff;
+	    }
+	  old_maglev_lb = vec_dup (ct->lb_maglev);
+
+	  cnat_translation_init_maglev (ct);
+	  cnat_maglev_print_changes (vm, changed_bk_indices, old_maglev_lb,
+				     ct->lb_maglev);
+
+	  vec_free (changed_bk_indices);
+	  vec_free (old_maglev_lb);
+	}
+    }
+
+  vec_foreach (ct, trs)
+    vec_free (ct->ct_active_paths);
+  vec_free (trs);
+
+  return (NULL);
+}
+
+VLIB_CLI_COMMAND (cnat_translation_test_init_maglev_cmd, static) = {
+  .path = "test cnat maglev",
+  .short_help = "test cnat maglev tests [n_tests] backends [num_backends] len "
+		"[maglev_len]",
+  .function = cnat_translation_test_init_maglev,
+};