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| author | Simon Marlow <marlowsd@gmail.com> | 2016-10-09 18:21:35 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2016-10-09 18:21:36 -0400 |
| commit | 85e81a850a3e79d965e18f267a0e0b1c4bc69fae (patch) | |
| tree | e3659426074078e2fce80b87253e6976373de0a5 /docs/users_guide/runtime_control.rst | |
| parent | 6c47f2efa3f8f4639f375d34f54c01a60c9a1a82 (diff) | |
| download | haskell-85e81a850a3e79d965e18f267a0e0b1c4bc69fae.tar.gz | |
Turn on -n4m with -A16m or greater
Nursery chunks help reduce the cost of GC when capabilities are unevenly
loaded, by ensuring that we use more of the available nursery.
The rationale for enabling this at -A16m is that any negative effects
due to loss of cache locality are less likely to be an issue at -A16m
and above. It's a conservative guess. If we had a lot of benchmark
data we could probably do better.
Results for nofib/parallel at -N4 -A32m with and without -n4m:
```
------------------------------------------------------------------------
Program Size Allocs Runtime Elapsed TotalMem
------------------------------------------------------------------------
blackscholes 0.0% -9.5% -9.0% -15.0% -2.2%
coins 0.0% -4.7% -3.6% -0.6% -13.6%
mandel 0.0% -0.3% +7.7% +13.1% +0.1%
matmult 0.0% +1.5% +10.0% +7.7% +0.1%
nbody 0.0% -4.1% -2.9% 0.085 0.0%
parfib 0.0% -1.4% +1.0% +1.5% +0.2%
partree 0.0% -0.3% +0.8% +2.9% -0.8%
prsa 0.0% -0.5% -2.1% -7.6% 0.0%
queens 0.0% -3.2% -1.4% +2.2% +1.3%
ray 0.0% -5.6% -14.5% -7.6% +0.8%
sumeuler 0.0% -0.4% +2.4% +1.1% 0.0%
------------------------------------------------------------------------
Min 0.0% -9.5% -14.5% -15.0% -13.6%
Max 0.0% +1.5% +10.0% +13.1% +1.3%
Geometric Mean +0.0% -2.6% -1.3% -0.5% -1.4%
```
Not conclusive, but slightly better. This matters a lot more when you
have more cores.
Test Plan: validate, nofib/paralel
Reviewers: niteria, ezyang, nh2, trofi, austin, erikd, bgamari
Reviewed By: bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2581
GHC Trac Issues: #9221
Diffstat (limited to 'docs/users_guide/runtime_control.rst')
| -rw-r--r-- | docs/users_guide/runtime_control.rst | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/docs/users_guide/runtime_control.rst b/docs/users_guide/runtime_control.rst index 0ffb1d8206..54c7508ba8 100644 --- a/docs/users_guide/runtime_control.rst +++ b/docs/users_guide/runtime_control.rst @@ -327,7 +327,7 @@ performance. .. rts-flag:: -n ⟨size⟩ - :default: 0 + :default: 4m with ``-A16m`` or larger, otherwise 0. .. index:: single: allocation area, chunk size |