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Diffstat (limited to 'docs/users_guide/runtime_control.rst')
| -rw-r--r-- | docs/users_guide/runtime_control.rst | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/docs/users_guide/runtime_control.rst b/docs/users_guide/runtime_control.rst index 5d3b24adac..49dc6a5441 100644 --- a/docs/users_guide/runtime_control.rst +++ b/docs/users_guide/runtime_control.rst @@ -420,7 +420,7 @@ performance. .. rts-flag:: -A ⟨size⟩ - :default: 1MB + :default: 4MB .. index:: single: allocation area, size @@ -429,15 +429,22 @@ performance. collector. The allocation area (actually generation 0 step 0) is fixed and is never resized (unless you use :rts-flag:`-H [⟨size⟩]`, below). - Increasing the allocation area size may or may not give better - performance (a bigger allocation area means worse cache behaviour - but fewer garbage collections and less promotion). + Optimal settings depend on the actual machine, program, and other RTS options. + Increasing the allocation area size means worse cache behaviour + but fewer garbage collections and less promotion. + + In general settings >= 4MB can reduce performance in some cases, in particular for single + threaded operation. However in a parallel setting increasing the allocation area + to ``16MB``, or even ``64MB`` can increase gc throughput significantly. With only 1 generation (e.g. ``-G1``, see :rts-flag:`-G ⟨generations⟩`) the ``-A`` option specifies the minimum allocation area, since the actual size of the allocation area will be resized according to the amount of data in the heap (see :rts-flag:`-F ⟨factor⟩`, below). + When heap profiling using a smaller allocation area can increase accuracy as more frequent + major garbage collections also results in more frequent heap snapshots + .. rts-flag:: -AL ⟨size⟩ :default: :rts-flag:`-A <-A ⟨size⟩>` value |