Debugging compile time, laptop vs server:

= Laptop:
Intel® Xeon® E3-1535M v5 (Quad Core 2.90GHz, 3.80GHz Turbo, 8MB 45W, w/Intel HD
Graphics P530)
32GB (2x16G) 2133MHz DDR4 ECC Memory

Linux ares 4.9.34-gentoo-kf0 #1 SMP Fri Jul 14 13:13:53 CEST 2017 x86_64 Intel(R) Xeon(R) CPU E3-1535M v5 @ 2.90GHz GenuineIntel GNU/Linux

SSD drives, but compiling happens in tmpfs anyways

# free -m
              total        used        free      shared  buff/cache   available
Mem:          32098        2172       28171          53        1754       29543
Swap:          1023           0        1023

# grep MAKE /etc/portage/make.conf
MAKEOPTS="-j10"

ares ~ # qlop -tHvg gcc
gcc-6.4.0: Sun Nov 26 16:36:01 2017: 27 minutes, 31 seconds
gcc-6.4.0: Tue Dec 12 23:37:08 2017: 29 minutes, 11 seconds

= Server:
2x Intel Xeon E5-2670 2.60GHz, 20M Cache, 8.0GT/s QPI, Turbo, 8C, 115W, DDR3-1600MHz
8x 16GB RDIMM, 1600MHz, Low Volt, Dual Rank, x4

Linux eta 4.9.16-gentoo-kf0 #1 SMP Fri Jun 2 00:39:51 CEST 2017 x86_64 Intel(R) Xeon(R) CPU E5-2670 0 @ 2.60GHz GenuineIntel GNU/Linux


# free -m
              total        used        free      shared  buff/cache   available
Mem:         128893       76271        5020        3499       47601       48216
Swap:         22889        7176       15713

Spinning drives in RAID-6, but compiling happens in tmpfs anyways

# grep MAKE /etc/portage/make.conf
MAKEOPTS="-j32"

# qlop -tHvg gcc
gcc-6.4.0: Sat Dec 16 19:22:43 2017: 38 minutes, 10 seconds
gcc-6.4.0: Sat Dec 16 21:48:03 2017: 38 minutes, 44 seconds
gcc-6.4.0: Thu Dec 21 16:30:44 2017: 37 minutes, 28 seconds

at -j10:
gcc-6.4.0: Thu Dec 21 18:10:12 2017: 41 minutes, 3 seconds

increasing  vm.dirty_expire_centisecs = 6000 (from 3000)