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| author | Simon Marlow <marlowsd@gmail.com> | 2016-10-09 18:20:53 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2016-10-09 18:21:16 -0400 |
| commit | 6c47f2efa3f8f4639f375d34f54c01a60c9a1a82 (patch) | |
| tree | e92395e5ef2530f9ea274e0f384426e70414b9db /docs | |
| parent | 8dc72f3c33b0e724ddb690c9d494969980c10afd (diff) | |
| download | haskell-6c47f2efa3f8f4639f375d34f54c01a60c9a1a82.tar.gz | |
Default +RTS -qn to the number of cores
Setting a -N value that is too large has a dramatic negative effect on
performance, but the new -qn flag can mitigate the worst of the effects
by limiting the number of GC threads.
So now, if you don't explcitly set +RTS -qn, and you set -N larger than
the number of cores (or use setNumCapabilities to do the same), we'll
default -qn to the number of cores.
These are the results from nofib/parallel on my 4-core (2 cores x 2
threads) i7 laptop, comparing -N8 before and after this change.
```
------------------------------------------------------------------------
Program Size Allocs Runtime Elapsed TotalMem
------------------------------------------------------------------------
blackscholes +0.0% +0.0% -72.5% -72.0% +9.5%
coins +0.0% -0.0% -73.7% -72.2% -0.8%
mandel +0.0% +0.0% -76.4% -75.4% +3.3%
matmult +0.0% +15.5% -26.8% -33.4% +1.0%
nbody +0.0% +2.4% +0.7% 0.076 0.0%
parfib +0.0% -8.5% -33.2% -31.5% +2.0%
partree +0.0% -0.0% -60.4% -56.8% +5.7%
prsa +0.0% -0.0% -65.4% -60.4% 0.0%
queens +0.0% +0.2% -58.8% -58.8% -1.5%
ray +0.0% -1.5% -88.7% -85.6% -3.6%
sumeuler +0.0% -0.0% -47.8% -46.9% 0.0%
------------------------------------------------------------------------
Min +0.0% -8.5% -88.7% -85.6% -3.6%
Max +0.0% +15.5% +0.7% -31.5% +9.5%
Geometric Mean +0.0% +0.6% -61.4% -63.1% +1.4%
```
Test Plan: validate, nofib/parallel benchmarks
Reviewers: niteria, ezyang, nh2, austin, erikd, trofi, bgamari
Reviewed By: trofi, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2580
GHC Trac Issues: #9221
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/runtime_control.rst | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/docs/users_guide/runtime_control.rst b/docs/users_guide/runtime_control.rst index 5226d6dc14..0ffb1d8206 100644 --- a/docs/users_guide/runtime_control.rst +++ b/docs/users_guide/runtime_control.rst @@ -467,7 +467,8 @@ performance. .. rts-flag:: -qn <x> - :default: the value of ``-N`` + :default: the value of ``-N`` or the number of CPU cores, + whichever is smaller. :since: 8.2.1 .. index:: |