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

[Bruce Richardson <bruce.richardson@intel.com>]

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?

/Bruce