Deadlock, Livelock, and Starvation

1
Deadlock, Livelock, and Starvation

• ???sta ?aµp???? ?.?. 127
• ???st?d????d?? ?a??a ?.?. 94

2
Deadlock Avoidance in Wormhole Switching

• Wormhole switching
• ?a??? de? ?p???e? pe?????sµ?? ??a t? µ??e??? t??
  pa??t??, t? pa??t? µp??e? ?a ?ata?aµß??e?
  pe??ss?te?a ap? ??a ?a????a ?ta? e??a?
  µp???a??sµ???
• ?p??e? ?a ?p?????? e?a?t?se?? ?a? µeta?? µ?
  ?e?t?????? ?a?a????
• ????t?s? ?a?a????
• ?s????? ?? e?a?t?se?? p?? ??????ta? sta SAF ?a?
  VCT switching
• ?st? ??a pa??t? p?? ?ata?aµß??e? ??a s?????
  ?e?t?????? ?a?a???? ci, ci1, , ck-1, ck, t?t??a
  ?ste ta ci ?a? ck e??a? escape channels, a??? ta
  ?p????pa ???
• Indirect dependency a? t? ci e??a? escape
  channel ??a t?? p?????sµ?
• Indirect cross-dependency a? t? ci de? e??a?
  escape channel ??a t?? p?????sµ?, a??? e??a? ??a
  ??p????? ?????? p?????sµ???

3
Deadlock Avoidance in Wormhole Switching

• ?a??de??µa 1

• ?a????a p?? e??????ta? ap? t?? ni ,
  ,

• ni t????? ??µß?? ?a? nj p?????sµ??

• S????t?s? d?ad??µ?s?? R a? ? t????? ??µß?? e??a?
  ? p?????sµ??, t?te ap????e?se t? pa??t?, a?????
  ???s?µ?p???se t?

• ?p?-s????t?s? d?ad??µ?s?? a? ? t????? ??µß??
  e??a? ? p?????sµ??, t?te ap????e?se t? pa??t?,
  a????? ???s?µ?p???se t?

4
Deadlock Avoidance in Wormhole Switching

• ?a??de??µa 1 (s????e?a)
• ? header ß??s?eta? st?? n1 ?a? p??????eta? ??a
  t?? n4
• ?p????? ?a a??????????? ta e??? µ???p?t?a
• cH1, cB2, cH3 ? indirect dependency
• cA1, cB2, cH3 ? indirect cross-dependency
• cA1, cA2, cH3 ? indirect cross-dependency (?a?
  direct cross-dependency ap? t? cA2 st? cH3)

5
Deadlock Avoidance in Wormhole Switching

• ?a??de??µa 2
• Ge?t?????? ??µß?? s??d???ta? µe d??
• ?a????a
• ?? n3 ?a? n0 s??d???ta? µe ??a ?a????
• ?a????a p?? e??????ta? ap? t?? ni cAi, i 0,
  1, 2, 3 ?a? cHi, i 0, 1, 2
• S????t?s? d?ad??µ?s?? R a? ? t????? ??µß?? e??a?
  ? p?????sµ??, t?te ap????e?se t? pa??t?, a?????
  ???s?µ?p???se t?
• ?p?-s????t?s? d?ad??µ?s?? a? ? t????? ??µß??
  e??a? ? p?????sµ??, t?te ap????e?se t? pa??t?,
  a????? ???s?µ?p???se t?

6
Deadlock Avoidance in Wormhole Switching

• ?a??de??µa 2 (s????e?a)
• ? header ß??s?eta? st?? n3 ?a? t? pa??t?
  p??????eta? ??a t?? n2
• ????p?t? cA3, cA0, cH1 ? indirect dependency
• ? header ß??s?eta? st?? n0 ?a?
• t? pa??t? p??????eta? ??a t?? n3
• ????p?t? cH0, cA1, cH2 ? indirect dependency
• Extended class dependency graph t?? R1 ??a
  wormhole switching
• ?a??? de? ?p?????? ??????, ? R e??a?
  deadlock-free ??a wormhole switching

7
Deadlock Avoidance in Wormhole Switching

• ?a?at???se??
• St? wormhole switching, ??a pa??t? µp??e? ?a
  ?ata?aµß??e? p???? ?a????a ?ta? ??e? µp?????e?
• ?at? s???pe?a, p????? s??a?t?se?? d?ad??µ?s??
  µp??e? ?a e??a? deadlock-free ??a t? SAF, a???
  ??? ??a t? wormhole switching
• ?pa??? ?????? se ??a extended channel dependency
  graph µ?a? s??dedeµ???? ?p?-s????t?s??
  d?ad??µ?s?? de s?µa??e? ?t? µp??e? ?a ?d????e? t?
  s?st?µa se ad????d?
• ?? de? ?p???e? ?????? se ?a???a ap? ta ??af?µata
  ???? t?? d??at?? ?p?-s??a?t?se?? d?ad??µ?s??, t?
  s?st?µa de? µp??e? ?a ?d????e? se ad????d?
• ?e? e??a? apa?a?t?t? ?a d???µ?s??µe ??e? t??
  ?p?-s??a?t?se?? d?ad??µ?s??. ???e? ?a ep??????µe
  µ?a st?? ?p??a? t? ???f?µa ?p???e? ?????? ?a? ?a
  p??spa??s??µe ?a de????µe ?t? µp????µe ?a
  ?d??????µe se ad????d?

8
Deadlock Avoidance in Wormhole Switching

• ?a??de??µa 3
• ????µa 2 d?ast?se?? ?p?? ???s?µ?p??e?ta? wormhole
  switching
• ???e f?s??? ?a???? ci a?t?st???e? se d?? e???????
  ?a????a ai ?a? bi
• ? s????t?s? d?ad??µ?s?? pa???e? ??a ta a ?a????a
  p?? a?????? st? e????st? µ???p?t? ?a? ??a b
  ?a???? s?µf??a µe t? dimension-order routing

9
Deadlock Avoidance in Wormhole Switching
?a????a t?? C1
?a????a
??a?t?se?? ?a?a????
?µµese? e?a?t?se?? ?a?a????

• ?a??de??µa 3 (s????e?a)

• C1 s????? t?? b ?a?a????
• R1
• ta ?a????a t?? C1 pa?????ta? ap? t?? R1 ??a
  ??p???? p?????sµ? a? ta pa???e? ?a? ? R (XY
  a??????µ?? d?ad??µ?s??)
• S??dedeµ???
• ?? ???f?µa e??a? ??????, ?p?te ? R e??a?
  deadlock-free

10
?pe?t?se??

• ???se?? ?a?a????
• St?? pe??ss?te?e? t?p?????e? µp????µe ?a ???s??µe
  µ?a d??ta?? µeta?? t?? ?a?a????
• ?s?d??aµa ?a????a e??a? d?? ?a????a p?? de?
  e??a? d?ad????? ?a? ????? ??????? p???????? ?a?
  ap??????? st? d??ta??
• ? s??s? a?t? d?µ?????e? t?? ???se?? ?s?d??aµ?a?
• ?eta?? ?a?a???? µ?a? ???s?? ?s?d??aµ?a? de?
  ?p?????? e?a?t?se??
• ????t?s? ???se?? d?? ???se?? e??a? e?a?t?µ??e?
  a? ?p?????? d?? ?a????a (??a ap? ???e µ?a) ta
  ?p??a e??a? e?a?t?µ??a
• ?? class dependency graph a?apa??st? t??
  e?a?t?se?? t?? ???se?? p?? pe??????? ??a ta
  ?a????a t?? d??t???
• ?? t? ???f?µa pe????e? µ??? t?? e?a?t?se?? t??
  ???se?? t?? ?a?a???? p?? pa???e? ? R1, t?te
  ???µ??eta? extended class dependency graph

11
?pe?t?se??

• ???se?? ?a?a????
• Te???µa µ?a s??dedeµ??? s????t?s? d?ad??µ?s?? R
  e??a? deadlock-free a? ?p???e? µ?a s??dedeµ???
  ?p?-s????t?s? d?ad??µ?s?? R1 ?a? µ?a s?s??t?s? R1
  ???sµ??? st? s?????
  ,
• t?t??a ?ste t? extended class dependency graph
  ??a t?? R1 ?a µ?? pe????e? ???????
• ? s?????? e??a? µ??? ??a??, a??? e??a? a??et? ??a
  ?a ap?de????µe deadlock freedom

12
?pe?t?se??

• ?pe?te????ta? t? ped?? ???sµ?? t?? s????t?s??
  d?ad??µ?s??
• ???s?µ?p????µe ep?p???? p????f???a
• ?.?. d?at????µe st? header t?? a???µ? t??
  ?a??asµ???? d?ad??µ?se?? p?? ????? ???e?
• Overhead
• ?.?. d?at????µe p????f???a ??a t? ?a???? e?s?d??,
  ?p?te t? ped?? ???sµ?? ???eta? C x N
• ?e?a??te?? e?e????a st?? ???sµ? s??a?t?se??
  d?ad??µ?s??
• ??p??e? configurations p?? µp????? ?a ?d???s???
  se ad????d? e??a? a??f??te?
• ?e?t????? ?????
• ?at? t? d?ad??µ?s? e??? pa??t??, ? s????t?s?
  d?ad??µ?s?? de? pa???e? ??a s????? ?a?a????, a???
  ??a s????? ????? (central queues)
• ?????? p???? e??a? ?? ?e?t????? ?????
• ????t?s? µeta?? d?? ????? ?p???e? ?ta? ??a pa??t?
  ß??s?eta? ????? ? µe???? se µ?a ap? a?t?? ?a?
  ??t? t?? ????
• ??t?st???a, ????eta? ? queue dependency graph
• Ge???e?s?
• ??a ?a???? ? µ?a ?e?t???? ???? e??a? ? p????
• ??t?st???a, ????eta? t? extended resource
  dependency graph

13
??a??a?t???? p??se???se??

• Te???t???? p??se???se??
• Deflection Routing
• Injection Limitation

14
Te???t???? p??se???se??

• Waiting channel
• ??a pa??t? ??e? desµe?se? ??p??a ?a????a, e??
  pe??µ??e? ??a ??p??a ???a
• ????e?ta? ??a ?a????a p?? a?????? se ??a
  ?p?s????? t?? ?a?a???? p?? pa?????ta? ap? t?
  s????t?s? d?ad??µ?s?? ??a a?t? t? pa??t?
• ?? t? pa??t? ??e? µp?????e?, ? a???µ?? t??
  ep?????? d?ad??µ?s?? µe???eta?
• ?s?d??aµe? µe t? d??aµ??? a??a?? t?? s????t?s??
  d?ad??µ?s?? ß?se? t?? ?at?stas?? t?? pa??t??
• ?ts? µp????µe ?a ap?f????µe ??p??e? ep?????? p??
  ?a µp????sa? ?a ?d???s??? se ad????d?
• ?????eta? ? e?e????a ?at? t? d?ad??µ?s?

15
Te???t???? p??se???se??

• Wait-for graph
• ?a? de???e? p????? p????? pe??µ????? ta
  µp???a??sµ??a pa??ta
• ?? ta µp???a??sµ??a pa??ta d?µ???????? ????? st?
  ???f?µa, t?te ?p???e????ta? ?a ???s?µ?p???s???
  ?tete?µ???st??? d?ad??µ?s?
• Message flow model
• ??a ta ?a????a p??pe? ?a e??a? deadlock-immune,
  d??ad? ?a e?????ta? t?? pa??d?s? t?? pa??t?? p??
  ta ??e? desµe?se?
• ??????, a?a????ta? ta ?a????a p?? e?????ta? t??
  pa??d?s? t?? pa??t??
• Se ???e ß?µa a?a????ta? ta ?a????a p?? e??a?
  ?e?t????? a?t?? p?? a?a?????a? st? p??????µe??
  ß?µa

16
Te???t???? p??se???se??

• Channel waiting graph
• ?e???e? t?? s?s?et?se?? µeta?? t?? ?a?a????
• ???s?µ?p??e?ta? ??? µ??? ? s????t?s? d?ad??µ?s??,
  a??? ?a? ? s????t?s? ep??????, µe ap?t??esµa ?a
  ?aµß??eta? ?p??? ?a? ? ?at?stas? t?? ?a?a???? t??
  d??t???
• Te???µa ? a??????µ?? d?ad??µ?s?? e??a?
  deadlock-free a? ?a? µ??? a? ?p???e? ??a
  wait-connected restricted channel waiting graph
  p?? de? ??e? a???????? ???????
• Wait-connected e??a? connected ???s?µ?p????ta?
  µ??? waiting channels
• True cycle ?????? p?? µp??e? ?a d?µ???????e?
  ?e?????ta? ap? ??a ?de?? d??t??

17
Deflection (Hot Potato) Routing

• ?d?a ? a???µ?? t?? e?se???µe??? ?a?a???? e??a?
  ?s?? µe t?? a???µ? t?? e?e???µe??? ?a?a????
• ?p?µ????, ??a e?se???µe?? pa??t? ß??s?e? p??t?te
  ??a e?e??e?? e?e???µe?? ?a????
• ?? ?p?????? pe??ss?te?a ap? ??a e?e??e?a ?a????a,
  ep????eta? e?e??? p?? a???e? st? e????st?
  µ???p?t?
• ?? ??a ta e?e???µe?a ?a????a e??a? desµe?µ??a,
  ???s?µ?p??e?ta? t? memory port, p?? e??a?
  e?e??e??
• ?p?µe?a pa??ta ap????e???ta? se buffer µ???? ?a
  ???e? d??at? ? ap?st??? t???
• ?e?????sµ??
• ?ta? ??a ta e?e???µe?a ?a????a e??a?
  apas????µ??a, t? pa??t? ap????e?eta? st??
  t?????ta ??µß?
• ?ta? ??a ta e?e???µe?a ?a????a p?? a?????? se
  e????sta µ???p?t?a e??a? apas????µ??a, t? pa??t?
  d??µ????e?ta? ?a??asµ??a
• ????s? t?? ?a??st???s?? pa??t??
• ?p??e? ?a ?d???se? se livelock
• ?p??t?ta, e?e????a

18
Injection Limitation

• ?fa?µ??eta? µ??? st?? te?????? SAF ?a? VCT
• ?a?t?????
• Se pe??pt?s? ad?e??d??, ?a???a pa??t? de? µp??e?
  ?a p??????e?
• ?e d?µ?????e?ta? ad????d? a? ?p???e? t??????st??
  µ?a ?de?a ??s? se ??a buffer t?? da?t?????
• ??? t? pet??a????µe ??a? ??µß?? de? ep?t??peta?
  ?a ap?ste??e? ??a pa??t? a? a?t? ?eµ??e? t??
  t?p??? t?? ????
• ???e ??µß?? ???s?µ?p??e? µ??? t?p??? p????f???a

19
Injection Limitation

• ?a??de??µa
• ? ??µß?? 1 de? µp??e? ?a ap?ste??e? pa??ta,
  epe?d? ? t?p??? t?? ???? e??a? ?eµ?t?. ??e?
  ?eµ?se? µet? ap? µetaf??? ded?µ???? ap? t?? ??µß?
  0
• ? ??µß?? 2 de? µp??e? ?a ap?ste??e? pa??ta epe?d?
  ?a ?eµ?se? ? t?p??? t?? ????
• ?? ??µß?? 0 ?a? 3 µp????? ?a ap?ste????? pa??ta

20
Injection Limitation

• Tori
• ?p?????? ?e?t????? ?????
• ?a ?a????a e??a? d??ate?????µe?a
• ?fa?µ??eta? dimension-order routing
• ???e ???? ?aµß??e? pa??ta ap? t?? t?p??? ??µß?
  ?a? ap? ?aµ???te?e? d?ast?se??
• ??a? ??µß?? de? ep?t??peta? ?a ap?ste??e? ??a
  pa??t? a? a?t? ?eµ??e? t?? a?t?st???? ????
• ??a pa??t? de? µp??e? ?a µetafe??e? st?? ep?µe??
  d??stas? a? ?eµ??e? t?? ???? p?? a?t?st???e? se
  a?t? t? d??stas?
• ? µ??a??sµ?? µp??e? ?a efa?µ?ste? ?a? se p???µata

21
Deadlock Avoidance in Switch-Based Networks

• ? d?a??pt?? µp??e? ?a s??d?eta? se ?a???a?, ??a?
  ? pe??ss?te???? epe?e??ast??, se a?t??es? µe ta
  Direct Networks, ?p?? ???e router s??d?eta? µe
  ??a? epe?e??ast?
• ??a??????µe d?? pe??pt?se??
• ? epa?a?????f???a ep?t??peta?
• ?fa?µ????ta? ta ?d?a ?e???t??? ap?te??sµata, ?p??
  ?a? st?? pe??pt?s? t?? Direct Networks
• ? epa?a?????f???a de? ep?t??peta?
• ?a pa??ta p???????ta? ap? a??ste?? p??? ta de???,
  µ?s? d?ad?????? stad???
• ?p?????? µ??? e?a?t?se?? a??µesa sta ?a????a d??
  d?ad?????? stad???
• ?e? ?p???e? ??????? e???t?s? a??µesa sta ?a????a
  µ? d?ad?????? stad???
• ?p?µ????, ap?fe????ta? ta ad????da

22
Deadlock Avoidance in Switch-Based Networks

• ???sµ?? ???se??
• ??????ta? t?se? ???se??, ?sa ?a? ta st?d?a, ?a???
  de? ?p?????? e?a?t?se?? a??µesa sta ?a????a t??
  ?d??? stad???
• ?? extended class dependency graph de? pe????e?
  ???????, ?a??? de? ?p?????? e?a?t?se?? µeta??
  µ?a? ???s?? e??? stad??? ?a? t?? ???se?? p??
  a?t?st?????? se p??????µe?a st?d?a
• ???ate?????µe?a MINs
• ?a d??ate?????µe?a ?a????a ?e?????ta? d?? ap??
  ?a????a µ???? ?ate????s??
• ??af??et??? ?a????a ???s?µ?p?????ta? ??a t??
  d?af??et???? ?ate????se??, ep?µ????, ????eta?
  ?at? ??p??? t??p? µ?a f?s??? d??ta?? t?? stad???

23
Deadlock Prevention in Circuit Switching and PCS

• ?e?????? pa?eµp?d?s?? ad?e??d??
• ??sµe?s? ???? t?? apa?t??µe??? p???? (?a????a,
  buffers) p??? ???s?µ?p???????
• ???s?µ?p?????ta? st?? te?????? Circuit Switching
  ?a? PCS
• ? p??? ap?st???e? ??a probe ??a t?? e??a??d??s?
  t?? µ???pat???
• ?at?p??, ta ded?µ??a p???????ta? st?? p?????sµ?
• ?e? µp??e? ?a d?µ???????e? ad????d?, ?a??? ????
  ??
• apa?t??µe??? p???? ????? desµe?te? p??? t??
  ??a??? t?? µet?d?s?? t?? pa??t??
• ?? t? µ???p?t? de? µp??e? ?a d?µ???????e?,
  ???eta? ?p?s??d??µ?s? ?a? ape?e??e?????ta? ??
  desµe?µ???? p????
• ?? de? ep?t??peta? ? ?p?s??d??µ?s?, t? probe
  µp??e? ?a µp?????e?, ?p?te de ???s?µ?p?????ta?
  te?????? pa?eµp?d?s?? ad?e??d??, a??? ?? te??????
  ap?f???? p?? efa?µ????ta? st? Wormhole Switching