Re: --min-parallelism sets max parallelism too

[David Fifield <david () bamsoftware com>]

On Sun, Sep 02, 2007 at 09:45:23AM -0500, Kris Katterjohn wrote:
> On 9/2/07, David Fifield <david () bamsoftware com> wrote:
> > All this talk about parallelism made me look deeper into how its works.
> > And I found something a little surprising. Due to a quirk in how options
> > are processed, when you specify --min-parallelism without also
> > specifying --max-parallelism, the maximum parallelism is also set to the
> > minimum. In other words, the parallelism stays the same for the whole
> > scan, never dropping below the minimum but never rising above it either.
> >
> > The relevant code is in NmapOps.cc:
> >
> >         max_parallelism = 0;
> >
> >         ...
> >
> >         /* Prevent performance values from getting out of whack */
> >         if (min_parallelism > max_parallelism)
> >                 max_parallelism = min_parallelism;
> >
> > This assignment should only take place if max_parallelism has been
> > defined, I think. Or is this the intended behavior?
>
> Well, there is also this line above that:
>
>   if (max_parallelism && min_parallelism && (min_parallelism >
> max_parallelism)) {
>     fatal("--min-parallelism=%i must be less than or equal to
> --max-parallelism=%i",min_parallelism,max_parallelism);
>
> So if they are both set, and min > max, then it bails.
>
> But otherwise, max = min because you need to have max >= min and (I guess)
> you can't really gauge how much the user wants for a max.

Right, but when I set --min-parallelism, I expect the parallelism to
actually be able to increase above the minimum.

We can just use the convention that 0 for min_parallelism and
max_parallelism means "unset". The other parts of the code already work
that way. ultra_scan, for example, uses 300 for the maximum congestion
window if o.max_parallelism is 0.

Or else we could just initialize the maximum to be something huge like
100000, like what is already done with o.max_host_group_sz.

David Fifield

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