[GHC] #10728: Add e.g. "-N<=4" in addition to the fixed "-N4" and variable "-N" RTS options

[GHC]

#10728: Add e.g. "-N<=4" in addition to the fixed "-N4" and variable "-N" RTS
options
-------------------------------------+-------------------------------------
        Reporter:  rrnewton          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  7.10.2
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9221, #8224      |  Differential Rev(s):  Phab:D1650
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by hvr):

 Here's two less controversial variants to `-Nmax` I wouldn't object to:

  - `-maxN` (this follows common conventions for `max` used for upper-
 bounding, c.f. `find . -mindepth <n> -maxdepth <n>`
  - Use a single letter option, e.g. `-n <n>`; this follows current `+RTS
 --help` convention, c.f.
      {{{
 -M<size> Sets the maximum heap size (default unlimited)  Egs: -M256k -M1G
 -H<size> Sets the minimum heap size (default 0M)   Egs: -H24m  -H1G
      }}}


 For reference, here's the current output of `ghc +RTS --help` for GHC
 HEAD, where `-Nmax` clearly deviates from the existing naming conventions:

 {{{
 ghc: unknown RTS option: --help
 ghc:
 ghc: Usage: <prog> <args> [+RTS <rtsopts> | -RTS <args>] ... --RTS <args>
 ghc:
 ghc:    +RTS    Indicates run time system options follow
 ghc:    -RTS    Indicates program arguments follow
 ghc:   --RTS    Indicates that ALL subsequent arguments will be given to
 the
 ghc:            program (including any of these RTS flags)
 ghc:
 ghc: The following run time system options are available:
 ghc:
 ghc:   -?       Prints this message and exits; the program is not executed
 ghc:   --info   Print information about the RTS used by this program
 ghc:
 ghc:   -K<size>  Sets the maximum stack size (default: 80% of the heap)
 ghc:             Egs: -K32k -K512k -K8M
 ghc:   -ki<size> Sets the initial thread stack size (default 1k)  Egs:
 -ki4k -ki2m
 ghc:   -kc<size> Sets the stack chunk size (default 32k)
 ghc:   -kb<size> Sets the stack chunk buffer size (default 1k)
 ghc:
 ghc:   -A<size> Sets the minimum allocation area size (default 512k) Egs:
 -A1m -A10k
 ghc:   -n<size> Allocation area chunk size (0 = disabled, default: 0)
 ghc:   -O<size> Sets the minimum size of the old generation (default 1M)
 ghc:   -M<size> Sets the maximum heap size (default unlimited)  Egs:
 -M256k -M1G
 ghc:   -H<size> Sets the minimum heap size (default 0M)   Egs: -H24m  -H1G
 ghc:   -m<n>    Minimum % of heap which must be available (default 3%)
 ghc:   -G<n>    Number of generations (default: 2)
 ghc:   -c<n>    Use in-place compaction instead of copying in the oldest
 generation
 ghc:            when live data is at least <n>% of the maximum heap size
 set with
 ghc:            -M (default: 30%)
 ghc:   -c       Use in-place compaction for all oldest generation
 collections
 ghc:            (the default is to use copying)
 ghc:   -w       Use mark-region for the oldest generation (experimental)
 ghc:   -I<sec>  Perform full GC after <sec> idle time (default: 0.3, 0 ==
 off)
 ghc:
 ghc:   -T         Collect GC statistics (useful for in-program statistics
 access)
 ghc:   -t[<file>] One-line GC statistics (if <file> omitted, uses stderr)
 ghc:   -s[<file>] Summary  GC statistics (if <file> omitted, uses stderr)
 ghc:   -S[<file>] Detailed GC statistics (if <file> omitted, uses stderr)
 ghc:
 ghc:
 ghc:   -Z       Don't squeeze out update frames on stack overflow
 ghc:   -B       Sound the bell at the start of each garbage collection
 ghc:
 ghc:   -h       Heap residency profile (output file <program>.hp)
 ghc:   -i<sec>  Time between heap profile samples (seconds, default: 0.1)
 ghc:
 ghc:   -C<secs>  Context-switch interval in seconds.
 ghc:             0 or no argument means switch as often as possible.
 ghc:             Default: 0.02 sec.
 ghc:   -V<secs>  Master tick interval in seconds (0 == disable timer).
 ghc:             This sets the resolution for -C and the heap profile
 timer -i,
 ghc:             and is the frequence of time profile samples.
 ghc:             Default: 0.01 sec.
 ghc:
 ghc:   -N[<n>]   Use <n> processors (default: 1, -N alone determines
 ghc:             the number of processors to use automatically)
 ghc:   -qg[<n>]  Use parallel GC only for generations >= <n>
 ghc:             (default: 0, -qg alone turns off parallel GC)
 ghc:   -qb[<n>]  Use load-balancing in the parallel GC only for
 generations >= <n>
 ghc:             (default: 1, -qb alone turns off load-balancing)
 ghc:   -qa       Use the OS to set thread affinity (experimental)
 ghc:   -qm       Don't automatically migrate threads between CPUs
 ghc:   -qi<n>    If a processor has been idle for the last <n> GCs, do not
 ghc:             wake it up for a non-load-balancing parallel GC.
 ghc:             (0 disables,  default: 0)
 ghc:   --install-signal-handlers=<yes|no>
 ghc:             Install signal handlers (default: yes)
 ghc:   -e<n>     Maximum number of outstanding local sparks (default:
 4096)
 ghc:   -xm       Base address to mmap memory in the GHCi linker
 ghc:             (hex; must be <80000000)
 ghc:   -xq       The allocation limit given to a thread after it receives
 ghc:             an AllocationLimitExceeded exception. (default: 100k)
 ghc:
 ghc: RTS options may also be specified using the GHCRTS environment
 variable.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10728#comment:15>
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