Unclear documentation about .eventlog's spark information flag

[shelarcy]

Unclear documentation about .eventlog's spark information flag

GHC 7.4.1 RC 1 User's Guide just describes that -l option's p flag enable/disable sampled result and f enable/disable flag fully accurate result.

• http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/runtime-control.html#rts-eventlog

But when enabled f without enabled p flag, .eventlog file doesn't have any useful information about sparks.

$ ./ParallelTest +RTS -l-af

$ ./ParallelTest +RTS -l-pf

If f flag requires p flag, please document that or change f flag's behavior.

[igloo]

Thanks for the report

[duncan]

I cannot reproduce the behaviour. It works correctly for me with ghc-7.4.1.

Using +RTS -l-af means we get no events (-a) except for the detailed spark events (f) (and default ones like capset) and indeed that's what we get with ghc-7.4.1.

e.g.

./parlist +RTS  -l-af
ghc-events show parlist.eventlog | less

[..snip...]
  1841000: cap 0: spark created
  1842000: cap 0: spark created
  1843000: cap 0: spark created
  1844000: cap 0: spark created
  1845000: cap 0: spark created

Using +RTS -l-pf means we get the default set of events, though without sampled spark events (-p), and with detailed spark events (f) and again, that's just what we do see with ghc-7.4.1.

./parlist +RTS  -l-pf
ghc-events show parlist.eventlog | less

[..snip...]
  2471000: cap 0: thread 2 is runnable
  2504000: cap 0: running thread 3
  2729000: cap 0: spark created
  2733000: cap 0: spark created

If you're seeing something different, or you still think the behaviour or documentation are confusing then please reopen the ticket. Thanks.

This is only a guess, but perhaps you've got an old version of ghc-events that does not show the detailed spark events. Does the ghc-events show produce this header:

  34: Spark counters (size 56)
  35: Spark create (size 0)
  36: Spark dud (size 0)
  37: Spark overflow (size 0)
  38: Spark run (size 0)
  39: Spark steal (size 2)
  40: Spark fizzle (size 0)
  41: Spark GC (size 0)

Where my log says cap 0: spark created, perhaps yours says something like cap 0: event 35.