Re: git bisect on multiple cores

[Matthieu Moy <Matthieu.Moy@imag.fr>]

Karl Hasselström <kha@treskal.com> writes:

> On 2008-04-08 12:58:47 +0200, A B wrote:
>
>> git bisect is really cool. I use it for the first time. Just a
>> thought, if you have a multiple core computer, can't you make git
>> build new versions in the background while testing the previuos
>> version? Alright, if you build 2 versions, one of them will never be
>> tested, but you will perhaps save some time by letting it build in
>> the background?
>
> Adding parallelism to a binary search scales very badly -- I'd say
> about logarithmically, but I haven't thought hard about it. If it's
> possible to use the extra cores to speed up the build+test cycle,
> that's vastly preferable.

Probably logarithmically with the number of cores. But for reasonable
machines, this number is relatively low, so the log is not so costly.
For a binary search, using just 2 cores, you can try the next in the
list in case of a "git bisect good" for example, and if the hypothesis
is true, you've just gained a factor 2 (assuming it happens 50% of
times, that should be a 50% speedup). Similarly, you should get a
factor 2 with 3 cores.

And as said before, you can also try trisection or N-section. But no,
I won't claim this is simple to implement ;-).

-- 
Matthieu