Re: [PATCH 0/4] make it possible to skip away from broken commits

[Christian Couder <chriscool@tuxfamily.org>]

Le Wednesday 03 June 2009, H. Peter Anvin a écrit :
> Junio C Hamano wrote:
> > Christian Couder <chriscool@tuxfamily.org> writes:
> >> This patch series adds a "--ratio=x/y" option to "git bisect skip" so
> >> that it is possible to skip away from an area were the commits cannot
> >> be tested.
> >>
> >> Note that in this series "--ratio=4" means the same as "--ratio=1/4".
> >> But I am not sure if this shortcut is worth it.
> >
> > Actually my gut feeling is that a tweakable knob itself is worth it,
> > because the user can never tell what the right value should be.
> >
> > Especially without any documentation updates that explains what this
> > ratio refers to ;-), but I suspect, unless the user is very familiar
> > with how the revision graph bisection internally works, such an
> > explanation would not help him find a skip ratio that is closer to the
> > optimum than a random guess.  Why not use a constant ratio (or perhaps
> > a pair of alternating ratios) on "bisect skip" without any new options?
>
> I would agree with this assessment.  It's hard enough to teach a user
> how to use "git bisect" as it is... and being able to have a *user*
> bisect a problem is worth its weight in gold.
>
> If the algorithm I proposed earlier is too complex, here is a very
> simple approximation:
>
> start:
> 	num = 1
> 	den = 2
>
> again:
> 	run test (num/den)
> 	if (!skip)
> 		goto start
>
> 	num = num + 2
> 	if (num > den)
> 		num = 1
> 		den = den * 2
>
> 	goto again
>
>
> This creates test ratios in the following sequence:
>
> 1/2 1/4 3/4 1/8 3/8 5/8 7/8 1/16 3/16 ...
>
> When one gets down to a small number of points this could get weird, but
> as long as skip points are filtered (which looks like it's already being
>  done) it should converge.

I agree. I will have a look.

Thanks,
Christian.