summaryrefslogtreecommitdiffstats
path: root/src/vnet/fib/fib_walk.c
blob: 6a64d554f98906ab345aa2bc90d1c65af04e1328 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
/*
 * Copyright (c) 2016 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <vnet/fib/fib_walk.h>
#include <vnet/fib/fib_node_list.h>

vlib_log_class_t fib_walk_logger;

/**
 * The flags on a walk
 */
typedef enum fib_walk_flags_t_
{
    /**
     * A synchronous walk.
     * This walk will run to completion, i.e. visit ALL the children.
     * It is a depth first traversal of the graph.
     */
    FIB_WALK_FLAG_SYNC = (1 << 0),
    /**
     * An asynchronous walk.
     * This walk will be scheduled to run in the background. It will thus visits
     * the children at a later point in time.
     * It is a depth first traversal of the graph.
     */
    FIB_WALK_FLAG_ASYNC = (1 << 1),
    /**
     * An indication that the walk is currently executing.
     */
    FIB_WALK_FLAG_EXECUTING = (1 << 2),
} fib_walk_flags_t;

/**
 * A representation of a graph walk from a parent object to its children
 */
typedef struct fib_walk_t_
{
    /**
     * FIB node linkage. This object is not in the FIB object graph,
     * but it is present in other node's dependency lists, so it needs to
     * be pointerable to.
     */
    fib_node_t fw_node;

    /**
     * the walk's flags
     */
    fib_walk_flags_t fw_flags;

    /**
     * Sibling index in the dependency list
     */
    u32 fw_dep_sibling;

    /**
     * Sibling index in the list of all walks
     */
    u32 fw_prio_sibling;

    /**
     * Pointer to the node whose dependants this walk is walking
     */
    fib_node_ptr_t fw_parent;

    /**
     * Number of nodes visited by this walk. saved for debugging purposes.
     */
    u32 fw_n_visits;

    /**
     * Time the walk started
     */
    f64 fw_start_time;

    /**
     * The reasons this walk is occuring.
     * This is a vector ordered in time. The reasons and the front were started
     * first, and so should be acted first when a node is visisted.
     */
    fib_node_back_walk_ctx_t *fw_ctx;
} fib_walk_t;

/**
 * @brief The pool of all walk objects
 */
static fib_walk_t *fib_walk_pool;

/**
 * Statistics maintained per-walk queue
 */
typedef enum fib_walk_queue_stats_t_
{
    FIB_WALK_SCHEDULED,
    FIB_WALK_COMPLETED,
} fib_walk_queue_stats_t;
#define FIB_WALK_QUEUE_STATS_NUM ((fib_walk_queue_stats_t)(FIB_WALK_COMPLETED+1))

#define FIB_WALK_QUEUE_STATS {           \
    [FIB_WALK_SCHEDULED] = "scheduled",  \
    [FIB_WALK_COMPLETED] = "completed",  \
}

#define FOR_EACH_FIB_WALK_QUEUE_STATS(_wqs)   \
    for ((_wqs) = FIB_WALK_SCHEDULED;         \
	 (_wqs) < FIB_WALK_QUEUE_STATS_NUM;   \
	 (_wqs)++)

/**
 * The names of the walk stats
 */
static const char * const fib_walk_queue_stats_names[] = FIB_WALK_QUEUE_STATS;
/**
 * The names of the walk reasons
 */
static const char * const fib_node_bw_reason_names[] = FIB_NODE_BW_REASONS;

/**
 * A represenation of one queue of walk
 */
typedef struct fib_walk_queue_t_
{
    /**
     * Qeuee stats
     */
    u64 fwq_stats[FIB_WALK_QUEUE_STATS_NUM];

    /**
     * The node list which acts as the queue
     */
    fib_node_list_t fwq_queue;
} fib_walk_queue_t;

/**
 * A set of priority queues for outstanding walks
 */
typedef struct fib_walk_queues_t_
{
    fib_walk_queue_t fwqs_queues[FIB_WALK_PRIORITY_NUM];
} fib_walk_queues_t;

/**
 * The global queues of outstanding walks
 */
static fib_walk_queues_t fib_walk_queues;

/**
 * The names of the walk priorities
 */
static const char * const fib_walk_priority_names[] = FIB_WALK_PRIORITIES;

/**
 * @brief Histogram stats on the lenths of each walk in elemenets visisted.
 * Store upto 1<<23 elements in increments of 1<<10
 */
#define HISTOGRAM_VISITS_PER_WALK_MAX (1<<23)
#define HISTOGRAM_VISITS_PER_WALK_INCR (1<<10)
#define HISTOGRAM_VISITS_PER_WALK_N_BUCKETS \
    (HISTOGRAM_VISITS_PER_WALK_MAX/HISTOGRAM_VISITS_PER_WALK_INCR)
static u64 fib_walk_hist_vists_per_walk[HISTOGRAM_VISITS_PER_WALK_N_BUCKETS];

/**
 * @brief History of state for the last 128 walks
 */
#define HISTORY_N_WALKS 128
#define MAX_HISTORY_REASONS 16
static u32 history_last_walk_pos;
typedef struct fib_walk_history_t_ {
    u32 fwh_n_visits;
    f64 fwh_duration;
    f64 fwh_completed;
    fib_node_ptr_t fwh_parent;
    fib_walk_flags_t fwh_flags;
    fib_node_bw_reason_flag_t fwh_reason[MAX_HISTORY_REASONS];
} fib_walk_history_t;
static fib_walk_history_t fib_walk_history[HISTORY_N_WALKS];

static u8* format_fib_walk (u8* s, va_list *ap);

#define FIB_WALK_DBG(_walk, _fmt, _args...)                     \
{                                                               \
    vlib_log_debug(fib_walk_logger,                             \
                   "[%U]:" _fmt,                                \
                   format_fib_walk,                             \
                   fib_walk_get_index(_walk),                   \
                   ##_args);                                    \
}

u8*
format_fib_walk_priority (u8 *s, va_list *ap)
{
    fib_walk_priority_t prio = va_arg(*ap, fib_walk_priority_t);

    ASSERT(prio < FIB_WALK_PRIORITY_NUM);

    return (format(s, "%s", fib_walk_priority_names[prio]));
}
static u8*
format_fib_walk_queue_stats (u8 *s, va_list *ap)
{
    fib_walk_queue_stats_t wqs = va_arg(*ap, fib_walk_queue_stats_t);

    ASSERT(wqs < FIB_WALK_QUEUE_STATS_NUM);

    return (format(s, "%s", fib_walk_queue_stats_names[wqs]));
}

static index_t
fib_walk_get_index (fib_walk_t *fwalk)
{
    return (fwalk - fib_walk_pool);
}

static fib_walk_t *
fib_walk_get (index_t fwi)
{
    return (pool_elt_at_index(fib_walk_pool, fwi));
}

/*
 * not static so it can be used in the unit tests
 */
u32
fib_walk_queue_get_size (fib_walk_priority_t prio)
{
    return (fib_node_list_get_size(fib_walk_queues.fwqs_queues[prio].fwq_queue));
}

static fib_node_index_t
fib_walk_queue_get_front (fib_walk_priority_t prio)
{
    fib_node_ptr_t wp;

    fib_node_list_get_front(fib_walk_queues.fwqs_queues[prio].fwq_queue, &wp);

    return (wp.fnp_index);
}

static void
fib_walk_destroy (index_t fwi)
{
    fib_walk_t *fwalk;
    u32 bucket, ii;

    fwalk = fib_walk_get(fwi);

    if (FIB_NODE_INDEX_INVALID != fwalk->fw_prio_sibling)
    {
	fib_node_list_elt_remove(fwalk->fw_prio_sibling);
    }
    fib_node_child_remove(fwalk->fw_parent.fnp_type,
			  fwalk->fw_parent.fnp_index,
			  fwalk->fw_dep_sibling);

    /*
     * refetch the walk object. More walks could have been spawned as a result
     * of releasing the lock on the parent.
     */
    fwalk = fib_walk_get(fwi);

    /*
     * add the stats to the continuous histogram collection.
     */
    bucket = (fwalk->fw_n_visits / HISTOGRAM_VISITS_PER_WALK_INCR);
    bucket = (bucket >= HISTOGRAM_VISITS_PER_WALK_N_BUCKETS ?
	      HISTOGRAM_VISITS_PER_WALK_N_BUCKETS - 1 :
	      bucket);
    fib_walk_hist_vists_per_walk[bucket]++;

    /*
     * save stats to the recent history
     */

    fib_walk_history[history_last_walk_pos].fwh_n_visits =
	fwalk->fw_n_visits;
    fib_walk_history[history_last_walk_pos].fwh_completed =
	vlib_time_now(vlib_get_main());
    fib_walk_history[history_last_walk_pos].fwh_duration =
	fib_walk_history[history_last_walk_pos].fwh_completed -
        fwalk->fw_start_time;
    fib_walk_history[history_last_walk_pos].fwh_parent =
	fwalk->fw_parent;
    fib_walk_history[history_last_walk_pos].fwh_flags =
	fwalk->fw_flags;

    vec_foreach_index(ii, fwalk->fw_ctx)
    {
        if (ii < MAX_HISTORY_REASONS)
        {
            fib_walk_history[history_last_walk_pos].fwh_reason[ii] =
                fwalk->fw_ctx[ii].fnbw_reason;
        }
    }

    history_last_walk_pos = (history_last_walk_pos + 1) % HISTORY_N_WALKS;

    fib_node_deinit(&fwalk->fw_node);
    vec_free(fwalk->fw_ctx);
    pool_put(fib_walk_pool, fwalk);
}

/**
 * return code when advancing a walk
 */
typedef enum fib_walk_advance_rc_t_
{
    /**
     * The walk is complete
     */
    FIB_WALK_ADVANCE_DONE,
    /**
     * the walk has more work
     */
    FIB_WALK_ADVANCE_MORE,
    /**
     * The walk merged with the one in front
     */
    FIB_WALK_ADVANCE_MERGE,
} fib_walk_advance_rc_t;

/**
 * @brief Advance the walk one element in its work list
 */
static fib_walk_advance_rc_t
fib_walk_advance (fib_node_index_t fwi)
{
    fib_node_back_walk_rc_t wrc;
    fib_node_ptr_t sibling;
    fib_walk_t *fwalk;
    uint n_ctxs, ii;
    int more_elts;

    /*
     * this walk function is re-entrant - walks acan spawn walks.
     * fib_walk_t objects come from a pool, so they can realloc. we need
     * to retch from said pool at the appropriate times.
     */
    fwalk = fib_walk_get(fwi);

    more_elts = fib_node_list_elt_get_next(fwalk->fw_dep_sibling, &sibling);

    if (more_elts)
    {

        /*
         * loop through the backwalk contexts. This can grow in length
         * as walks on the same object meet each other. Order is preserved so the
         * most recently started walk as at the back of the vector.
         */
        ii = 0;
        n_ctxs = vec_len(fwalk->fw_ctx);

        while (ii < n_ctxs)
        {
	    wrc = fib_node_back_walk_one(&sibling, &fwalk->fw_ctx[ii]);

            ii++;
	    fwalk = fib_walk_get(fwi);
	    fwalk->fw_n_visits++;

	    if (FIB_NODE_BACK_WALK_MERGE == wrc)
	    {
		/*
		 * this walk has merged with the one further along the node's
		 * dependecy list.
		 */
		return (FIB_WALK_ADVANCE_MERGE);
	    }

            /*
             * re-evaluate the number of backwalk contexts we need to process.
             */
            n_ctxs = vec_len(fwalk->fw_ctx);
	}
	/*
	 * move foward to the next node to visit
	 */
	more_elts = fib_node_list_advance(fwalk->fw_dep_sibling);
    }

    if (more_elts)
    {
	return (FIB_WALK_ADVANCE_MORE);
    }

    return (FIB_WALK_ADVANCE_DONE);
}

/**
 * @breif Enurmerate the times of sleep between walks
 */
typedef enum fib_walk_sleep_type_t_
{
    FIB_WALK_SHORT_SLEEP,
    FIB_WALK_LONG_SLEEP,
} fib_walk_sleep_type_t;

#define FIB_WALK_N_SLEEP (FIB_WALK_LONG_SLEEP+1)

/**
 * @brief Durations for the sleep types
 */
static f64 fib_walk_sleep_duration[] = {
    /**
     * Long sleep when there is no more work, i.e. the queues are empty.
     * This is a sleep (as opposed to a wait for event) just to be sure we
     * are not missing events by sleeping forever.
     */
    [FIB_WALK_LONG_SLEEP] = 2,

    /**
     * Short sleep. There is work left in the queues. We are yielding the CPU
     * momentarily.
     */
    [FIB_WALK_SHORT_SLEEP] = 1e-8,
};

/**
 * @brief The time quota for a walk. When more than this amount of time is
 * spent, the walk process will yield.
 */
static f64 quota = 1e-4;

/**
 * Histogram on the amount of work done (in msecs) in each walk
 */
#define N_TIME_BUCKETS 128
#define TIME_INCREMENTS (N_TIME_BUCKETS/2)
static u64 fib_walk_work_time_taken[N_TIME_BUCKETS];

/**
 * Histogram on the number of nodes visted in each quota
 */
#define N_ELTS_BUCKETS 128
static u32 fib_walk_work_nodes_visisted_incr = 2;
static u64 fib_walk_work_nodes_visited[N_ELTS_BUCKETS];

/**
 * Histogram of the sleep lengths
 */
static u64 fib_walk_sleep_lengths[2];

/**
 * @brief Service the queues
 * This is not declared static so that it can be unit tested - i know i know...
 */
f64
fib_walk_process_queues (vlib_main_t * vm,
			 const f64 quota)
{
    f64 start_time, consumed_time;
    fib_walk_sleep_type_t sleep;
    fib_walk_priority_t prio;
    fib_walk_advance_rc_t rc;
    fib_node_index_t fwi;
    fib_walk_t *fwalk;
    u32 n_elts;
    i32 bucket;

    consumed_time = 0;
    start_time = vlib_time_now(vm);
    n_elts = 0;

    FOR_EACH_FIB_WALK_PRIORITY(prio)
    {
	while (0 != fib_walk_queue_get_size(prio))
	{
	    fwi = fib_walk_queue_get_front(prio);

	    /*
	     * set this walk as executing
	     */
	    fwalk = fib_walk_get(fwi);
	    fwalk->fw_flags |= FIB_WALK_FLAG_EXECUTING;

	    do
	    {
		rc = fib_walk_advance(fwi);
		n_elts++;
		consumed_time = (vlib_time_now(vm) - start_time);
	    } while ((consumed_time < quota) &&
		     (FIB_WALK_ADVANCE_MORE == rc));

	    /*
	     * if this walk has no more work then pop it from the queue
	     * and move on to the next.
	     */
	    if (FIB_WALK_ADVANCE_MORE != rc)
	    {
                fib_walk_destroy(fwi);
		fib_walk_queues.fwqs_queues[prio].fwq_stats[FIB_WALK_COMPLETED]++;
	    }
	    else
	    {
		/*
		 * passed our work quota. sleep time.
		 */
		fwalk = fib_walk_get(fwi);
		fwalk->fw_flags &= ~FIB_WALK_FLAG_EXECUTING;
		sleep = FIB_WALK_SHORT_SLEEP;
		goto that_will_do_for_now;
	    }
	}
    }
    /*
     * got to the end of all the work
     */
    sleep = FIB_WALK_LONG_SLEEP;

that_will_do_for_now:

    /*
     * collect the stats:
     *  - for the number of nodes visisted we store 128 increments
     *  - for the time consumed we store quota/TIME_INCREMENTS increments.
     */
    bucket = ((n_elts/fib_walk_work_nodes_visisted_incr) > N_ELTS_BUCKETS ?
	      N_ELTS_BUCKETS-1 :
	      n_elts/fib_walk_work_nodes_visisted_incr);
    ++fib_walk_work_nodes_visited[bucket];

    bucket = (consumed_time - quota) / (quota / TIME_INCREMENTS);
    bucket += N_TIME_BUCKETS/2;
    bucket = (bucket < 0 ? 0 : bucket);
    bucket = (bucket > N_TIME_BUCKETS-1 ? N_TIME_BUCKETS-1 : bucket);
    ++fib_walk_work_time_taken[bucket];

    ++fib_walk_sleep_lengths[sleep];

    return (fib_walk_sleep_duration[sleep]);
}

/**
 * Events sent to the FIB walk process
 */
typedef enum fib_walk_process_event_t_
{
    FIB_WALK_PROCESS_EVENT_DATA,
    FIB_WALK_PROCESS_EVENT_ENABLE,
    FIB_WALK_PROCESS_EVENT_DISABLE,
} fib_walk_process_event;

/**
 * @brief The 'fib-walk' process's main loop.
 */
static uword
fib_walk_process (vlib_main_t * vm,
		  vlib_node_runtime_t * node,
		  vlib_frame_t * f)
{
    uword event_type, *event_data = 0;
    f64 sleep_time;
    int enabled;

    enabled = 1;
    sleep_time = fib_walk_sleep_duration[FIB_WALK_SHORT_SLEEP];

    while (1)
    {
        /*
         * the feature to disable/enable this walk process is only
         * for testing purposes
         */
        if (enabled)
        {
            vlib_process_wait_for_event_or_clock(vm, sleep_time);
        }
        else
        {
            vlib_process_wait_for_event(vm);
        }

        event_type = vlib_process_get_events(vm, &event_data);
        vec_reset_length(event_data);

        switch (event_type)
	{
	case FIB_WALK_PROCESS_EVENT_ENABLE:
            enabled = 1;
            break;
	case FIB_WALK_PROCESS_EVENT_DISABLE:
            enabled = 0;
            break;
	default:
            break;
	}

        if (enabled)
        {
            sleep_time = fib_walk_process_queues(vm, quota);
        }
    }

    /*
     * Unreached
     */
    ASSERT(!"WTF");
    return 0;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (fib_walk_process_node,static) = {
    .function = fib_walk_process,
    .type = VLIB_NODE_TYPE_PROCESS,
    .name = "fib-walk",
};
/* *INDENT-ON* */

/**
 * @brief Allocate a new walk object
 */
static fib_walk_t *
fib_walk_alloc (fib_node_type_t parent_type,
		fib_node_index_t parent_index,
		fib_walk_flags_t flags,
		fib_node_back_walk_ctx_t *ctx)
{
    fib_walk_t *fwalk;

    pool_get(fib_walk_pool, fwalk);

    fib_node_init(&fwalk->fw_node, FIB_NODE_TYPE_WALK);

    fwalk->fw_flags = flags;
    fwalk->fw_dep_sibling  = FIB_NODE_INDEX_INVALID;
    fwalk->fw_prio_sibling = FIB_NODE_INDEX_INVALID;
    fwalk->fw_parent.fnp_index = parent_index;
    fwalk->fw_parent.fnp_type = parent_type;
    fwalk->fw_ctx = NULL;
    fwalk->fw_start_time = vlib_time_now(vlib_get_main());
    fwalk->fw_n_visits = 0;

    /*
     * make a copy of the backwalk context so the depth count remains
     * the same for each sibling visitsed. This is important in the case
     * where a parent has a loop via one child, but all the others are not.
     * if the looped child were visited first, the depth count would exceed, the
     * max and the walk would terminate before it reached the other siblings.
     */
    vec_add1(fwalk->fw_ctx, *ctx);

    return (fwalk);
}

/**
 * @brief Enqueue a walk onto the appropriate priority queue. Then signal
 * the background process there is work to do.
 */
static index_t
fib_walk_prio_queue_enquue (fib_walk_priority_t prio,
			    fib_walk_t *fwalk)
{
    index_t sibling;

    sibling = fib_node_list_push_front(fib_walk_queues.fwqs_queues[prio].fwq_queue,
				       0,
				       FIB_NODE_TYPE_WALK,
				       fib_walk_get_index(fwalk));
    fib_walk_queues.fwqs_queues[prio].fwq_stats[FIB_WALK_SCHEDULED]++;

    /*
     * poke the fib-walk process to perform the async walk.
     * we are not passing it specific data, hence the last two args,
     * the process will drain the queues
     */
    vlib_process_signal_event(vlib_get_main(),
			      fib_walk_process_node.index,
			      FIB_WALK_PROCESS_EVENT_DATA,
			      0);

    return (sibling);
}

void
fib_walk_async (fib_node_type_t parent_type,
		fib_node_index_t parent_index,
		fib_walk_priority_t prio,
		fib_node_back_walk_ctx_t *ctx)
{
    fib_walk_t *fwalk;

    if (FIB_NODE_GRAPH_MAX_DEPTH < ++ctx->fnbw_depth)
    {
	/*
	 * The walk has reached the maximum depth. there is a loop in the graph.
	 * bail.
	 */
	return;
    }
    if (0 == fib_node_get_n_children(parent_type,
                                     parent_index))
    {
        /*
         * no children to walk - quit now
         */
        return;
    }
    if (ctx->fnbw_flags & FIB_NODE_BW_FLAG_FORCE_SYNC)
    {
        /*
         * the originator of the walk wanted it to be synchronous, but the
         * parent object chose async - denied.
         */
        return (fib_walk_sync(parent_type, parent_index, ctx));
    }


    fwalk = fib_walk_alloc(parent_type,
			   parent_index,
			   FIB_WALK_FLAG_ASYNC,
			   ctx);

    fwalk->fw_dep_sibling = fib_node_child_add(parent_type,
					       parent_index,
					       FIB_NODE_TYPE_WALK,
					       fib_walk_get_index(fwalk));

    fwalk->fw_prio_sibling = fib_walk_prio_queue_enquue(prio, fwalk);

    FIB_WALK_DBG(fwalk, "async-start: %U",
                 format_fib_node_bw_reason, ctx->fnbw_reason);
}

/**
 * @brief Back walk all the children of a FIB node.
 *
 * note this is a synchronous depth first walk. Children visited may propagate
 * the walk to thier children. Other children node types may not propagate,
 * synchronously but instead queue the walk for later async completion.
 */
void
fib_walk_sync (fib_node_type_t parent_type,
	       fib_node_index_t parent_index,
	       fib_node_back_walk_ctx_t *ctx)
{
    fib_walk_advance_rc_t rc;
    fib_node_index_t fwi;
    fib_walk_t *fwalk;

    if (FIB_NODE_GRAPH_MAX_DEPTH < ++ctx->fnbw_depth)
    {
	/*
	 * The walk has reached the maximum depth. there is a loop in the graph.
	 * bail.
	 */
	return;
    }
    if (0 == fib_node_get_n_children(parent_type,
                                     parent_index))
    {
        /*
         * no children to walk - quit now
         */
        return;
    }

    fwalk = fib_walk_alloc(parent_type,
			   parent_index,
			   FIB_WALK_FLAG_SYNC,
			   ctx);

    fwalk->fw_dep_sibling = fib_node_child_add(parent_type,
					       parent_index,
					       FIB_NODE_TYPE_WALK,
					       fib_walk_get_index(fwalk));
    fwi = fib_walk_get_index(fwalk);
    FIB_WALK_DBG(fwalk, "sync-start: %U",
                 format_fib_node_bw_reason, ctx->fnbw_reason);

    while (1)
    {
	/*
	 * set this walk as executing
	 */
	fwalk->fw_flags |= FIB_WALK_FLAG_EXECUTING;

	do
	{
	    rc = fib_walk_advance(fwi);
	} while (FIB_WALK_ADVANCE_MORE == rc);


	/*
	 * this walk function is re-entrant - walks can spawn walks.
	 * fib_walk_t objects come from a pool, so they can realloc. we need
	 * to re-fetch from said pool at the appropriate times.
	 */
	fwalk = fib_walk_get(fwi);

	if (FIB_WALK_ADVANCE_MERGE == rc)
	{
	    /*
	     * this sync walk merged with an walk in front.
	     * by reqeusting a sync walk the client wanted all children walked,
	     * so we ditch the walk object in hand and continue with the one
	     * we merged into
	     */
	    fib_node_ptr_t merged_walk;

	    fib_node_list_elt_get_next(fwalk->fw_dep_sibling, &merged_walk);

	    ASSERT(FIB_NODE_INDEX_INVALID != merged_walk.fnp_index);
	    ASSERT(FIB_NODE_TYPE_WALK == merged_walk.fnp_type);

	    fib_walk_destroy(fwi);

	    fwi = merged_walk.fnp_index;
	    fwalk = fib_walk_get(fwi);

	    if (FIB_WALK_FLAG_EXECUTING & fwalk->fw_flags)
	    {
		/*
		 * we are executing a sync walk, and we have met with another
		 * walk that is also executing. since only one walk executs at once
		 * (there is no multi-threading) this implies we have met ourselves
		 * and hence the is a loop in the graph.
		 * This function is re-entrant, so the walk object we met is being
		 * acted on in a stack frame below this one. We must therefore not
		 * continue with it now, but let the stack unwind and along the
		 * appropriate frame to read the depth count and bail.
		 */
                FIB_WALK_DBG(fwalk, "sync-stop: %U",
                             format_fib_node_bw_reason,
                             ctx->fnbw_reason);

		fwalk = NULL;
		break;
	    }
	}
	else
	{
	    /*
	     * the walk reached the end of the depdency list.
	     */
	    break;
	}
    }

    if (NULL != fwalk)
    {
        FIB_WALK_DBG(fwalk, "sync-stop: %U",
                     format_fib_node_bw_reason,
                     ctx->fnbw_reason);
	fib_walk_destroy(fwi);
    }
}

static fib_node_t *
fib_walk_get_node (fib_node_index_t index)
{
    fib_walk_t *fwalk;

    fwalk = fib_walk_get(index);

    return (&(fwalk->fw_node));
}

/**
 * Walk objects are not parents, nor are they locked.
 * are no-ops
 */
static void
fib_walk_last_lock_gone (fib_node_t *node)
{
    ASSERT(0);
}

static fib_walk_t*
fib_walk_get_from_node (fib_node_t *node)
{
    return ((fib_walk_t*)(((char*)node) -
			  STRUCT_OFFSET_OF(fib_walk_t, fw_node)));
}

/**
 * @brief Another back walk has reach this walk.
 * Megre them so there is only one left. It is this node being
 * visited that will remain, so copy or merge the context onto it.
 */
static fib_node_back_walk_rc_t
fib_walk_back_walk_notify (fib_node_t *node,
			   fib_node_back_walk_ctx_t *ctx)
{
    fib_node_back_walk_ctx_t *last;
    fib_walk_t *fwalk;

    fwalk = fib_walk_get_from_node(node);

    /*
     * check whether the walk context can be merged with the most recent.
     * the most recent was the one last added and is thus at the back of the vector.
     * we can merge walks if the reason for the walk is the same.
     */
    last = vec_end(fwalk->fw_ctx) - 1;

    if (last->fnbw_reason == ctx->fnbw_reason)
    {
        /*
         * copy the largest of the depth values. in the presence of a loop,
         * the same walk will merge with itself. if we take the smaller depth
         * then it will never end.
         */
        last->fnbw_depth = ((last->fnbw_depth >= ctx->fnbw_depth) ?
                            last->fnbw_depth :
                            ctx->fnbw_depth);
    }
    else
    {
        /*
         * walks could not be merged, this means that the walk infront needs to
         * perform different action to this one that has caught up. the one in
         * front was scheduled first so append the new walk context to the back
         * of the list.
         */
        vec_add1(fwalk->fw_ctx, *ctx);
    }

    return (FIB_NODE_BACK_WALK_MERGE);
}

/**
 * The FIB walk's graph node virtual function table
 */
static const fib_node_vft_t fib_walk_vft = {
    .fnv_get = fib_walk_get_node,
    .fnv_last_lock = fib_walk_last_lock_gone,
    .fnv_back_walk = fib_walk_back_walk_notify,
};

void
fib_walk_module_init (void)
{
    fib_walk_priority_t prio;

    FOR_EACH_FIB_WALK_PRIORITY(prio)
    {
	fib_walk_queues.fwqs_queues[prio].fwq_queue = fib_node_list_create();
    }

    fib_node_register_type(FIB_NODE_TYPE_WALK, &fib_walk_vft);
    fib_walk_logger = vlib_log_register_class("fib", "walk");
}

static u8*
format_fib_walk (u8* s, va_list *ap)
{
    fib_node_index_t fwi = va_arg(*ap, fib_node_index_t);
    fib_walk_t *fwalk;

    fwalk = fib_walk_get(fwi);

    return (format(s, "[@%d] parent:{%s:%d} visits:%d flags:%d", fwi,
		   fib_node_type_get_name(fwalk->fw_parent.fnp_type),
		   fwalk->fw_parent.fnp_index,
		   fwalk->fw_n_visits,
		   fwalk->fw_flags));
}

u8 *
format_fib_node_bw_reason (u8 *s, va_list *args)
{
    fib_node_bw_reason_flag_t flag = va_arg (*args, int);
    fib_node_back_walk_reason_t reason;

    FOR_EACH_FIB_NODE_BW_REASON(reason) {
        if ((1<<reason) & flag)
            s = format(s, "%s", fib_node_bw_reason_names[reason]);
    }

    return (s);
}

static clib_error_t *
fib_walk_show (vlib_main_t * vm,
	       unformat_input_t * input,
	       vlib_cli_command_t * cmd)
{
    fib_walk_queue_stats_t wqs;
    fib_walk_priority_t prio;
    fib_node_ptr_t sibling;
    fib_node_index_t fwi;
    fib_walk_t *fwalk;
    int more_elts, ii;
    u8 *s = NULL;

#define USEC 1000000
    vlib_cli_output(vm, "FIB Walk Quota = %.2fusec:", quota * USEC);
    vlib_cli_output(vm, "FIB Walk queues:");

    FOR_EACH_FIB_WALK_PRIORITY(prio)
    {
	vlib_cli_output(vm, " %U priority queue:",
			format_fib_walk_priority, prio);
	vlib_cli_output(vm, "  Stats: ");

	FOR_EACH_FIB_WALK_QUEUE_STATS(wqs)
	{
	    vlib_cli_output(vm, "    %U:%d",
			    format_fib_walk_queue_stats, wqs,
			    fib_walk_queues.fwqs_queues[prio].fwq_stats[wqs]);
	}
	vlib_cli_output(vm, "  Occupancy:%d",
			fib_node_list_get_size(
			    fib_walk_queues.fwqs_queues[prio].fwq_queue));

	more_elts = fib_node_list_get_front(
			fib_walk_queues.fwqs_queues[prio].fwq_queue,
			&sibling);

	while (more_elts)
	{
	    ASSERT(FIB_NODE_INDEX_INVALID != sibling.fnp_index);
	    ASSERT(FIB_NODE_TYPE_WALK == sibling.fnp_type);

	    fwi = sibling.fnp_index;
	    fwalk = fib_walk_get(fwi);

	    vlib_cli_output(vm, "  %U", format_fib_walk, fwi);

	    more_elts = fib_node_list_elt_get_next(fwalk->fw_prio_sibling,
						   &sibling);
	}
    }

    vlib_cli_output(vm, "Histogram Statistics:");
    vlib_cli_output(vm, " Number of Elements visit per-quota:");
    for (ii = 0; ii < N_ELTS_BUCKETS; ii++)
    {
	if (0 != fib_walk_work_nodes_visited[ii])
	    s = format(s, "%d:%d ",
		       (ii * fib_walk_work_nodes_visisted_incr),
		       fib_walk_work_nodes_visited[ii]);
    }
    vlib_cli_output(vm, "  %v", s);
    vec_free(s);

    vlib_cli_output(vm, " Time consumed per-quota (Quota=%f usec):", quota*USEC);
    s = format(s, "0:%d ", fib_walk_work_time_taken[0]);
    for (ii = 1; ii < N_TIME_BUCKETS; ii++)
    {
	if (0 != fib_walk_work_time_taken[ii])
	    s = format(s, "%d:%d ", (u32)((((ii - N_TIME_BUCKETS/2) *
					   (quota / TIME_INCREMENTS)) + quota) *
					 USEC),
		       fib_walk_work_time_taken[ii]);
    }
    vlib_cli_output(vm, "  %v", s);
    vec_free(s);

    vlib_cli_output(vm, " Sleep Types:");
    vlib_cli_output(vm, "  Short  Long:");
    vlib_cli_output(vm, "  %d %d:",
		    fib_walk_sleep_lengths[FIB_WALK_SHORT_SLEEP],
		    fib_walk_sleep_lengths[FIB_WALK_LONG_SLEEP]);

    vlib_cli_output(vm, " Number of Elements visited per-walk:");
    for (ii = 0; ii < HISTOGRAM_VISITS_PER_WALK_N_BUCKETS; ii++)
    {
	if (0 != fib_walk_hist_vists_per_walk[ii])
	    s = format(s, "%d:%d ",
		       ii*HISTOGRAM_VISITS_PER_WALK_INCR,
		       fib_walk_hist_vists_per_walk[ii]);
    }
    vlib_cli_output(vm, "  %v", s);
    vec_free(s);


    vlib_cli_output(vm, "Brief History (last %d walks):", HISTORY_N_WALKS);
    ii = history_last_walk_pos - 1;
    if (ii < 0)
        ii = HISTORY_N_WALKS - 1;

    while (ii != history_last_walk_pos)
    {
	if (0 != fib_walk_history[ii].fwh_reason[0])
	{
            u8 *s = NULL;
            u32 jj;

	    s = format(s, "[@%d]: %s:%d visits:%d duration:%.2f completed:%.2f ",
                       ii, fib_node_type_get_name(fib_walk_history[ii].fwh_parent.fnp_type),
                       fib_walk_history[ii].fwh_parent.fnp_index,
                       fib_walk_history[ii].fwh_n_visits,
                       fib_walk_history[ii].fwh_duration,
                       fib_walk_history[ii].fwh_completed);
            if (FIB_WALK_FLAG_SYNC & fib_walk_history[ii].fwh_flags)
                s = format(s, "sync, ");
            if (FIB_WALK_FLAG_ASYNC & fib_walk_history[ii].fwh_flags)
                s = format(s, "async, ");

            s = format(s, "reason:");
            jj = 0;
            while (0 != fib_walk_history[ii].fwh_reason[jj])
            {
                s = format (s, "%U,", format_fib_node_bw_reason,
                            fib_walk_history[ii].fwh_reason[jj]);
                jj++;
            }
            vlib_cli_output(vm, "%v", s);
	}

        ii--;
        if (ii < 0)
            ii = HISTORY_N_WALKS - 1;
    }

    return (NULL);
}

VLIB_CLI_COMMAND (fib_walk_show_command, static) = {
    .path = "show fib walk",
    .short_help = "show fib walk",
    .function = fib_walk_show,
};

static clib_error_t *
fib_walk_set_quota (vlib_main_t * vm,
		    unformat_input_t * input,
		    vlib_cli_command_t * cmd)
{
    clib_error_t * error = NULL;
    f64 new_quota;

    if (unformat (input, "%f", &new_quota))
    {
	quota = new_quota;
    }
    else
    {
	error = clib_error_return(0 , "Pass a float value");
    }

    return (error);
}

VLIB_CLI_COMMAND (fib_walk_set_quota_command, static) = {
    .path = "set fib walk quota",
    .short_help = "set fib walk quota",
    .function = fib_walk_set_quota,
};

static clib_error_t *
fib_walk_set_histogram_elements_size (vlib_main_t * vm,
				      unformat_input_t * input,
				      vlib_cli_command_t * cmd)
{
    clib_error_t * error = NULL;
    u32 new;

    if (unformat (input, "%d", &new))
    {
	fib_walk_work_nodes_visisted_incr = new;
    }
    else
    {
	error = clib_error_return(0 , "Pass an int value");
    }

    return (error);
}

VLIB_CLI_COMMAND (fib_walk_set_histogram_elements_size_command, static) = {
    .path = "set fib walk histogram elements size",
    .short_help = "set fib walk histogram elements size",
    .function = fib_walk_set_histogram_elements_size,
};

static clib_error_t *
fib_walk_clear (vlib_main_t * vm,
		unformat_input_t * input,
		vlib_cli_command_t * cmd)
{
    memset(fib_walk_hist_vists_per_walk, 0, sizeof(fib_walk_hist_vists_per_walk));
    memset(fib_walk_history, 0, sizeof(fib_walk_history));
    memset(fib_walk_work_time_taken, 0, sizeof(fib_walk_work_time_taken));
    memset(fib_walk_work_nodes_visited, 0, sizeof(fib_walk_work_nodes_visited));
    memset(fib_walk_sleep_lengths, 0, sizeof(fib_walk_sleep_lengths));

    return (NULL);
}

VLIB_CLI_COMMAND (fib_walk_clear_command, static) = {
    .path = "clear fib walk",
    .short_help = "clear fib walk",
    .function = fib_walk_clear,
};

void
fib_walk_process_enable (void)
{
    vlib_process_signal_event(vlib_get_main(),
                              fib_walk_process_node.index,
                              FIB_WALK_PROCESS_EVENT_ENABLE,
                              0);
}

void
fib_walk_process_disable (void)
{
    vlib_process_signal_event(vlib_get_main(),
                              fib_walk_process_node.index,
                              FIB_WALK_PROCESS_EVENT_DISABLE,
                              0);
}

static clib_error_t *
fib_walk_process_enable_disable (vlib_main_t * vm,
                                 unformat_input_t * input,
                                 vlib_cli_command_t * cmd)
{
    if (unformat (input, "enable"))
    {
        fib_walk_process_enable();
    }
    else if (unformat (input, "disable"))
    {
        fib_walk_process_disable();
    }
    else
    {
        return clib_error_return(0, "choose enable or disable");
    }
    return (NULL);
}

VLIB_CLI_COMMAND (fib_walk_process_command, static) = {
    .path = "test fib-walk-process",
    .short_help = "test fib-walk-process [enable|disable]",
    .function = fib_walk_process_enable_disable,
};