[bug] "git bisect old v3.0" takes 21 mins on Linux repo

Hi. This is bug report. "git bisect" is unacceptable slow on Linux repo.

Steps to reproduce:

===
d-user@comp:/tmp/t$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Cloning into 'linux'...
remote: Enumerating objects: 13079335, done.
remote: Counting objects: 100% (153/153), done.
remote: Compressing objects: 100% (108/108), done.
remote: Total 13079335 (delta 84), reused 70 (delta 45), pack-reused 13079182
Receiving objects: 100% (13079335/13079335), 5.18 GiB | 13.72 MiB/s, done.
Resolving deltas: 100% (10454171/10454171), done.
Updating files: 100% (87234/87234), done.
d-user@comp:/tmp/t$ cd linux
d-user@comp:/tmp/t/linux$ git bisect start
status: waiting for both good and bad commits
d-user@comp:/tmp/t/linux$ git bisect new v6.13-rc7
status: waiting for good commit(s), bad commit known
d-user@comp:/tmp/t/linux$ time -p git bisect old v3.0
Bisecting: 535608 revisions left to test after this (roughly 19 steps)
[62606c224d72a98c35d21a849f95cccf95b0a252] Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6
real 1293.32
user 1291.70
sys 1.41
===

1293.32 s (21 mins) is unacceptably slow. During "git bisect" execution process "git bisect--helper" occupies 100 % of CPU in "htop" output. (This means that "git bisect--helper" is not parallel program, overwise it would occupy significantly more than 100 %).

So, please, make "git bisect" faster. (Maybe it makes sence to make it parallel?)

My OS is Debian 12 Bookworm. Output of "uname -a" is "Linux comp 6.1.0-28-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.119-1 (2024-11-22) x86_64 GNU/Linux".

My git version is 2.39.5.

The above test was performed on tmpfs on real hardware without any kind of virtualization.

I will try to perform the same test with latest git version and will report my findings in the next mail (hopefully today).

-- Askar Safin https://types.pl/@safinaskar