I search the old source codes by what I have boxes XIAOMI R3G and YouHua WR1200JS whose WIFI 5Fhz worked well in 4.14.102 but more in 4.14.115?
the goal would be to find the modified version that caused this
jeff@deb-devel:~/devel/openwrt$ git log --pretty=oneline | fgrep 'bump 4.14 to 4.14.1'
6c3584b61c kernel: bump 4.14 to 4.14.119
09050b6fe2 kernel: bump 4.14 to 4.14.118
07720c392f kernel: bump 4.14 to 4.14.115
b765f4be40 kernel: bump 4.14 to 4.14.114
07aaa7e3d6 kernel: bump 4.14 to 4.14.113
da5bd73d70 kernel: bump 4.14 to 4.14.112
5387bc9cbb kernel: bump 4.14 to 4.14.111
5eac37624f kernel: bump 4.14 to 4.14.110
968baed351 kernel: bump 4.14 to 4.14.109
af6c86dbe5 kernel: bump 4.14 to 4.14.108
0304e76cd1 kernel: bump 4.14 to 4.14.107
a8cfef6c45 kernel: bump 4.14 to 4.14.106
364ab348dc kernel: bump 4.14 to 4.14.105
1cfbf95393 kernel: bump 4.14 to 4.14.104
ceed0665cc kernel: bump 4.14 to 4.14.103
3a2668c6d5 kernel: bump 4.14 to 4.14.102
[...]
Perhaps faster than using git bisect blindly.
openwrt$ git log --pretty=oneline 3a2668c6d5..07720c392f | wc -l
526
526 > 2^9 so I'd expect 9 or 10 tests to locate first good/bad commit between those two end points.