scripts/h0: use -j2 at GHC_OPTS

[root]

Created by: andriytk

According to the test resuts on 12 CPU Cores devvm
it is the most optimal building parameter.

Test script:

$ cat test-stack-build-perf.sh
set -xe

cd ~/halon
git clean -dfx
GHC_OPTS=-g /usr/bin/time scripts/h0 make
git clean -dfx
GHC_OPTS=-g /usr/bin/time scripts/h0 make -j4
git clean -dfx
GHC_OPTS=-g /usr/bin/time scripts/h0 make -j8
git clean -dfx
GHC_OPTS='-g -j2' /usr/bin/time scripts/h0 make
git clean -dfx
GHC_OPTS='-g -j4' /usr/bin/time scripts/h0 make
git clean -dfx
GHC_OPTS='-g -j8' /usr/bin/time scripts/h0 make
git clean -dfx
GHC_OPTS='-g -j' /usr/bin/time scripts/h0 make

Test results:

$ cat test-stack-build-perf.res.txt | egrep -A1 'GHC|CPU'

• GHC_OPTS=-g
• /usr/bin/time scripts/h0 make
  --
  997.55user 105.22system 14:47.39elapsed 124%CPU (0avgtext+0avgdata 2953972maxresident)k
  413016inputs+8194672outputs (69major+17575775minor)pagefaults 0swaps
  --
• GHC_OPTS=-g
• /usr/bin/time scripts/h0 make -j4
  --
  1013.68user 77.95system 14:36.90elapsed 124%CPU (0avgtext+0avgdata 2973704maxresident)k
  0inputs+8194736outputs (0major+17739726minor)pagefaults 0swaps
  --
• GHC_OPTS=-g
• /usr/bin/time scripts/h0 make -j8
  --
  1019.39user 69.69system 14:35.63elapsed 124%CPU (0avgtext+0avgdata 3041760maxresident)k
  0inputs+8194784outputs (0major+17491205minor)pagefaults 0swaps
  --
• GHC_OPTS='-g -j2'
• /usr/bin/time scripts/h0 make
  --
  1123.75user 199.35system 11:49.11elapsed 186%CPU (0avgtext+0avgdata 3283796maxresident)k
  0inputs+8197112outputs (0major+18539123minor)pagefaults 0swaps
  --
• GHC_OPTS='-g -j4'
• /usr/bin/time scripts/h0 make
  --
  1505.71user 534.26system 11:49.39elapsed 287%CPU (0avgtext+0avgdata 3443920maxresident)k
  0inputs+8197424outputs (0major+18539768minor)pagefaults 0swaps
  --
• GHC_OPTS='-g -j8'
• /usr/bin/time scripts/h0 make
  --
  4601.90user 1610.50system 16:55.32elapsed 611%CPU (0avgtext+0avgdata 3409816maxresident)k
  0inputs+8197592outputs (0major+18611415minor)pagefaults 0swaps
  --
• GHC_OPTS='-g -j'
• /usr/bin/time scripts/h0 make
  --
  14217.42user 5387.23system 33:58.51elapsed 961%CPU (0avgtext+0avgdata 3459492maxresident)k
  0inputs+8197760outputs (0major+18699674minor)pagefaults 0swaps

See also commercialhaskell/stack#644.

[root]

Created by: vvv

Landed as ca911e7.