Re: [PATCH v2 0/3] allow easier use of high lcore-ids

[David Marchand <david.marchand@redhat.com>]

Hello Bruce,

On Tue, Apr 1, 2025 at 4:08 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> On Mon, Mar 24, 2025 at 05:30:26PM +0000, Bruce Richardson wrote:
> > Traditionally, DPDK has had a direct mapping of internal lcore-ids, to
> > the actual core numbers in use. With higher core count servers becoming
> > more prevalent the issue becomes one of increasing memory footprint when
> > using such a scheme, due to the need to have all arrays dimensioned for
> > all cores on the system, whether or not those cores are in use by the
> > app.
> >
> > Therefore, the decision was made in the past to not expand the
> > build-time RTE_MAX_LCORE value beyond 128. Instead, it was recommended
> > that users use the "--lcores" EAL parameter to take the high-numbered
> > cores they wish to use and map them to lcore-ids within the 0 - 128
> > range. While this works, this is a little clunky as it means that
> > instead of just passing, for example, "-l 130-139", the user must
> > instead pass "--lcores 0@130,1@131,2@132,3@133,...."
> >
> > This patchset attempts to simplify the situation by adding a new flag to
> > do this mapping automatically. To use cores 130-139 and map them to ids
> > 0-9 internally, the EAL args now become: "-l 130-139 --map-lcore-ids",
> > or using the shorter "-M" version of the flag: "-Ml 130-139".
> >
> > Adding this new parameter required some rework of the existing arg
> > parsing code, because in current DPDK the args are parsed and checked in
> > the order they appear on the commandline. This means that using the
> > example above, the core parameter 130-139 will be rejected immediately
> > before the "map-lcore-ids" parameter is seen. To work around this, the
> > core (and service core) parameters are not parsed when seen, instead
> > they are only saved off and parsed after all arguments are parsed. The
> > "-l" and "-c" parameters are converted into "--lcores" arguments, so all
> > assigning of lcore ids is done there in all cases.
> >
> > RFC->v2:
> > * converted printf to DEBUG log
> > * added "-M" as shorter version of flag
> > * added documentation
> > * renamed internal API that was changed to avoid any potential hidden
> >   runtime issues.
> >
> > Bruce Richardson (3):
> >   eal: centralize core parameter parsing
> >   eal: convert core masks and lists to core sets
> >   eal: allow automatic mapping of high lcore ids
> >
> Ping for review.
>
> At a high level, does this feature seem useful to users?

This seems useful, though I am not I would touch the existing options.
I would have gone with a simple -L option (taking the same kind of
input than -l but with new behavior), and not combine a flag with
existing options.

I scanned through the series, not much to say.
Maybe add a unit test for new cmdline option.



-- 
David Marchand