Documentation/bpf/map_lru_hash_update.dot

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 // Copyright (C) 2022-2023 Isovalent, Inc.
   3 digraph {
   4   node [colorscheme=accent4,style=filled] # Apply colorscheme to all nodes
   5   graph [splines=ortho, nodesep=1]
   6
   7   subgraph cluster_key {
   8     label = "Key\n(locks held during operation)";
   9     rankdir = TB;
  10
  11     remote_lock [shape=rectangle,fillcolor=4,label="remote CPU LRU lock"]
  12     hash_lock [shape=rectangle,fillcolor=3,label="hashtab lock"]
  13     lru_lock [shape=rectangle,fillcolor=2,label="LRU lock"]
  14     local_lock [shape=rectangle,fillcolor=1,label="local CPU LRU lock"]
  15     no_lock [shape=rectangle,label="no locks held"]
  16   }
  17
  18   begin [shape=oval,label="begin\nbpf_map_update()"]
  19
  20   // Nodes below with an 'fn_' prefix are roughly labeled by the C function
  21   // names that initiate the corresponding logic in kernel/bpf/bpf_lru_list.c.
  22   // Number suffixes and errno suffixes handle subsections of the corresponding
  23   // logic in the function as of the writing of this dot.
  24
  25   // cf. __local_list_pop_free() / bpf_percpu_lru_pop_free()
  26   local_freelist_check [shape=diamond,fillcolor=1,
  27     label="Local freelist\nnode available?"];
  28   use_local_node [shape=rectangle,
  29     label="Use node owned\nby this CPU"]
  30
  31   // cf. bpf_lru_pop_free()
  32   common_lru_check [shape=diamond,
  33     label="Map created with\ncommon LRU?\n(!BPF_F_NO_COMMON_LRU)"];
  34
  35   fn_bpf_lru_list_pop_free_to_local [shape=rectangle,fillcolor=2,
  36     label="Flush local pending,
  37     Rotate Global list, move
  38     LOCAL_FREE_TARGET
  39     from global -> local"]
  40   // Also corresponds to:
  41   // fn__local_list_flush()
  42   // fn_bpf_lru_list_rotate()
  43   fn___bpf_lru_node_move_to_free[shape=diamond,fillcolor=2,
  44     label="Able to free\nLOCAL_FREE_TARGET\nnodes?"]
  45
  46   fn___bpf_lru_list_shrink_inactive [shape=rectangle,fillcolor=3,
  47     label="Shrink inactive list
  48       up to remaining
  49       LOCAL_FREE_TARGET
  50       (global LRU -> local)"]
  51   fn___bpf_lru_list_shrink [shape=diamond,fillcolor=2,
  52     label="> 0 entries in\nlocal free list?"]
  53   fn___bpf_lru_list_shrink2 [shape=rectangle,fillcolor=2,
  54     label="Steal one node from
  55       inactive, or if empty,
  56       from active global list"]
  57   fn___bpf_lru_list_shrink3 [shape=rectangle,fillcolor=3,
  58     label="Try to remove\nnode from hashtab"]
  59
  60   local_freelist_check2 [shape=diamond,label="Htab removal\nsuccessful?"]
  61   common_lru_check2 [shape=diamond,
  62     label="Map created with\ncommon LRU?\n(!BPF_F_NO_COMMON_LRU)"];
  63
  64   subgraph cluster_remote_lock {
  65     label = "Iterate through CPUs\n(start from current)";
  66     style = dashed;
  67     rankdir=LR;
  68
  69     local_freelist_check5 [shape=diamond,fillcolor=4,
  70       label="Steal a node from\nper-cpu freelist?"]
  71     local_freelist_check6 [shape=rectangle,fillcolor=4,
  72       label="Steal a node from
  73         (1) Unreferenced pending, or
  74         (2) Any pending node"]
  75     local_freelist_check7 [shape=rectangle,fillcolor=3,
  76       label="Try to remove\nnode from hashtab"]
  77     fn_htab_lru_map_update_elem [shape=diamond,
  78       label="Stole node\nfrom remote\nCPU?"]
  79     fn_htab_lru_map_update_elem2 [shape=diamond,label="Iterated\nall CPUs?"]
  80     // Also corresponds to:
  81     // use_local_node()
  82     // fn__local_list_pop_pending()
  83   }
  84
  85   fn_bpf_lru_list_pop_free_to_local2 [shape=rectangle,
  86     label="Use node that was\nnot recently referenced"]
  87   local_freelist_check4 [shape=rectangle,
  88     label="Use node that was\nactively referenced\nin global list"]
  89   fn_htab_lru_map_update_elem_ENOMEM [shape=oval,label="return -ENOMEM"]
  90   fn_htab_lru_map_update_elem3 [shape=rectangle,
  91     label="Use node that was\nactively referenced\nin (another?) CPU's cache"]
  92   fn_htab_lru_map_update_elem4 [shape=rectangle,fillcolor=3,
  93     label="Update hashmap\nwith new element"]
  94   fn_htab_lru_map_update_elem5 [shape=oval,label="return 0"]
  95   fn_htab_lru_map_update_elem_EBUSY [shape=oval,label="return -EBUSY"]
  96   fn_htab_lru_map_update_elem_EEXIST [shape=oval,label="return -EEXIST"]
  97   fn_htab_lru_map_update_elem_ENOENT [shape=oval,label="return -ENOENT"]
  98
  99   begin -> local_freelist_check
 100   local_freelist_check -> use_local_node [xlabel="Y"]
 101   local_freelist_check -> common_lru_check [xlabel="N"]
 102   common_lru_check -> fn_bpf_lru_list_pop_free_to_local [xlabel="Y"]
 103   common_lru_check -> fn___bpf_lru_list_shrink_inactive [xlabel="N"]
 104   fn_bpf_lru_list_pop_free_to_local -> fn___bpf_lru_node_move_to_free
 105   fn___bpf_lru_node_move_to_free ->
 106     fn_bpf_lru_list_pop_free_to_local2 [xlabel="Y"]
 107   fn___bpf_lru_node_move_to_free ->
 108     fn___bpf_lru_list_shrink_inactive [xlabel="N"]
 109   fn___bpf_lru_list_shrink_inactive -> fn___bpf_lru_list_shrink
 110   fn___bpf_lru_list_shrink -> fn_bpf_lru_list_pop_free_to_local2 [xlabel = "Y"]
 111   fn___bpf_lru_list_shrink -> fn___bpf_lru_list_shrink2 [xlabel="N"]
 112   fn___bpf_lru_list_shrink2 -> fn___bpf_lru_list_shrink3
 113   fn___bpf_lru_list_shrink3 -> local_freelist_check2
 114   local_freelist_check2 -> local_freelist_check4 [xlabel = "Y"]
 115   local_freelist_check2 -> common_lru_check2 [xlabel = "N"]
 116   common_lru_check2 -> local_freelist_check5 [xlabel = "Y"]
 117   common_lru_check2 -> fn_htab_lru_map_update_elem_ENOMEM [xlabel = "N"]
 118   local_freelist_check5 -> fn_htab_lru_map_update_elem [xlabel = "Y"]
 119   local_freelist_check5 -> local_freelist_check6 [xlabel = "N"]
 120   local_freelist_check6 -> local_freelist_check7
 121   local_freelist_check7 -> fn_htab_lru_map_update_elem
 122
 123   fn_htab_lru_map_update_elem -> fn_htab_lru_map_update_elem3 [xlabel = "Y"]
 124   fn_htab_lru_map_update_elem -> fn_htab_lru_map_update_elem2  [xlabel = "N"]
 125   fn_htab_lru_map_update_elem2 ->
 126     fn_htab_lru_map_update_elem_ENOMEM [xlabel = "Y"]
 127   fn_htab_lru_map_update_elem2 -> local_freelist_check5 [xlabel = "N"]
 128   fn_htab_lru_map_update_elem3 -> fn_htab_lru_map_update_elem4
 129
 130   use_local_node -> fn_htab_lru_map_update_elem4
 131   fn_bpf_lru_list_pop_free_to_local2 -> fn_htab_lru_map_update_elem4
 132   local_freelist_check4 -> fn_htab_lru_map_update_elem4
 133
 134   fn_htab_lru_map_update_elem4 -> fn_htab_lru_map_update_elem5 [headlabel="Success"]
 135   fn_htab_lru_map_update_elem4 ->
 136     fn_htab_lru_map_update_elem_EBUSY [xlabel="Hashtab lock failed"]
 137   fn_htab_lru_map_update_elem4 ->
 138     fn_htab_lru_map_update_elem_EEXIST [xlabel="BPF_EXIST set and\nkey already exists"]
 139   fn_htab_lru_map_update_elem4 ->
 140     fn_htab_lru_map_update_elem_ENOENT [headlabel="BPF_NOEXIST set\nand no such entry"]
 141
 142   // Create invisible pad nodes to line up various nodes
 143   pad0 [style=invis]
 144   pad1 [style=invis]
 145   pad2 [style=invis]
 146   pad3 [style=invis]
 147   pad4 [style=invis]
 148
 149   // Line up the key with the top of the graph
 150   no_lock -> local_lock [style=invis]
 151   local_lock -> lru_lock [style=invis]
 152   lru_lock -> hash_lock [style=invis]
 153   hash_lock -> remote_lock [style=invis]
 154   remote_lock -> local_freelist_check5 [style=invis]
 155   remote_lock -> fn___bpf_lru_list_shrink [style=invis]
 156
 157   // Line up return code nodes at the bottom of the graph
 158   fn_htab_lru_map_update_elem -> pad0 [style=invis]
 159   pad0 -> pad1 [style=invis]
 160   pad1 -> pad2 [style=invis]
 161   //pad2-> fn_htab_lru_map_update_elem_ENOMEM [style=invis]
 162   fn_htab_lru_map_update_elem4 -> pad3 [style=invis]
 163   pad3 -> fn_htab_lru_map_update_elem5  [style=invis]
 164   pad3 -> fn_htab_lru_map_update_elem_EBUSY  [style=invis]
 165   pad3 -> fn_htab_lru_map_update_elem_EEXIST  [style=invis]
 166   pad3 -> fn_htab_lru_map_update_elem_ENOENT  [style=invis]
 167
 168   // Reduce diagram width by forcing some nodes to appear above others
 169   local_freelist_check4 -> fn_htab_lru_map_update_elem3 [style=invis]
 170   common_lru_check2 -> pad4 [style=invis]
 171   pad4 -> local_freelist_check5 [style=invis]
 172 }