diff options
| -rw-r--r-- | docs/users_guide/using-concurrent.rst | 8 | ||||
| -rw-r--r-- | rts/RtsFlags.c | 17 |
2 files changed, 20 insertions, 5 deletions
diff --git a/docs/users_guide/using-concurrent.rst b/docs/users_guide/using-concurrent.rst index c00a294132..2621afce0f 100644 --- a/docs/users_guide/using-concurrent.rst +++ b/docs/users_guide/using-concurrent.rst @@ -107,11 +107,14 @@ RTS options for SMP parallelism There are two ways to run a program on multiple processors: call ``Control.Concurrent.setNumCapabilities`` from your program, or use the -RTS ``-N`` option. +RTS ``-N`` options. ``-N⟨x⟩`` +``-Nmax⟨x⟩`` + .. index:: single: -N⟨x⟩; RTS option + single: -Nmax(x); RTS option Use ⟨x⟩ simultaneous threads when running the program. @@ -133,6 +136,9 @@ RTS ``-N`` option. value of ⟨x⟩ itself based on how many processors are in your machine. + With Nmax⟨x⟩, i.e. ``+RTS -Nmax3 -RTS``, the runtime will choose at + most (x), also limited by the number of processors on the system. + Be careful when using all the processors in your machine: if some of your processors are in use by other programs, this can actually harm performance rather than improve it. diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c index 94572792de..bd60591f33 100644 --- a/rts/RtsFlags.c +++ b/rts/RtsFlags.c @@ -391,8 +391,9 @@ usage_text[] = { "", #endif /* DEBUG */ #if defined(THREADED_RTS) && !defined(NOSMP) -" -N[<n>] Use <n> processors (default: 1, -N alone determines", -" the number of processors to use automatically)", +" -N[<n>] Use <n> processors (default: 1, -N alone determines", +" the number of processors to use automatically)", +" -Nmax[<n>] Use up to n processors automatically", " -qg[<n>] Use parallel GC only for generations >= <n>", " (default: 0, -qg alone turns off parallel GC)", " -qb[<n>] Use load-balancing in the parallel GC only for generations >= <n>", @@ -1041,13 +1042,21 @@ error = rtsTrue; } else { int nNodes; OPTION_SAFE; /* but see extra checks below... */ - nNodes = strtol(rts_argv[arg]+2, (char **) NULL, 10); + + // <=n feature request ticket #10728 + if (strncmp("max", &rts_argv[arg][2], 3) == 0) { + int proc = (int)getNumberOfProcessors(); + nNodes = strtol(rts_argv[arg]+5, (char **) NULL, 10); + if (nNodes > proc) { nNodes = proc; } + } else { + nNodes = strtol(rts_argv[arg]+2, (char **) NULL, 10); + } if (nNodes <= 0) { errorBelch("bad value for -N"); error = rtsTrue; } if (rtsOptsEnabled == RtsOptsSafeOnly && - nNodes > (int)getNumberOfProcessors()) { + nNodes > (int)getNumberOfProcessors()) { errorRtsOptsDisabled("Using large values for -N is not allowed by default. %s"); stg_exit(EXIT_FAILURE); } |