Re: [PATCH v3 1/4] eal: deprecate old coremask-based EAL parameters

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri,  2 May 2025 16:11:31 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> As the number of cores/cpus on platforms has increased over the years,
> the use of coremasks rather than core-lists for identifying DPDK cores
> has become more and more unwieldy. At this point, let's deprecate the
> coremask-based EAL parameters for future removal, and point users to the
> core-list based versions instead.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

Agree.

There are some more syntax options on Linux kernel command line:
https://github.com/torvalds/linux/blob/master/Documentation/admin-guide/kernel-parameters.rst#cpu-lists

cpu lists
Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, nohz_full, irqaffinity, rcu_nocbs. The format of this list is:

<cpu number>,...,<cpu number>
or

<cpu number>-<cpu number> (must be a positive range in ascending order)
or a mixture

<cpu number>,...,<cpu number>-<cpu number>

Note that for the special case of a range one can split the range into equal sized groups and for each group use some amount from the beginning of that group:

<cpu number>-<cpu number>:<used size>/<group size>
For example one can add to the command line following parameter:

isolcpus=1,2,10-20,100-2000:2/25
where the final item represents CPUs 100,101,125,126,150,151,...

The value "N" can be used to represent the numerically last CPU on the system, i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.

Keep in mind that "N" is dynamic, so if system changes cause the bitmap width to change, such as less cores in the CPU list, then N and any ranges using N will also change. Use the same on a small 4 core system, and "16-N" becomes "16-3" and now the same boot input will be flagged as invalid (start > end).

The special case-tolerant group name "all" has a meaning of selecting all CPUs, so that "nohz_full=all" is the equivalent of "nohz_full=0-N".

The semantics of "N" and "all" is supported on a level of bitmaps and holds for all users of bitmap_parselist().