[PATCH v2 0/3] allow easier use of high lcore-ids
Bruce Richardson
bruce.richardson at intel.com
Mon Apr 7 17:38:40 CEST 2025
On Mon, Apr 07, 2025 at 08:14:50AM -0700, Stephen Hemminger wrote:
> On Mon, 7 Apr 2025 12:15:13 +0200
> Morten Brørup <mb at smartsharesystems.com> wrote:
>
> > > From: Bruce Richardson [mailto:bruce.richardson at intel.com]
> > > Sent: Monday, 7 April 2025 11.49
> > >
> > > On Mon, Apr 07, 2025 at 09:04:05AM +0200, David Marchand wrote:
> > > > Hello Bruce,
> > > >
> > > > On Tue, Apr 1, 2025 at 4:08 PM Bruce Richardson
> > > > <bruce.richardson at 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 at 130,1 at 131,2 at 132,3 at 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.
> > > >
> > >
> > > That would be an easier patchset to do up. However, it would then mean
> > > that
> > > we have no less than 4 different ways to specify the cores to use: "-
> > > c",
> > > "-l", "-L", "--lcores" - and therefore need 4 different sets of parsing
> > > options for them, and more checks to ensure we have only one of the 4
> > > specified in any run. That's why I chose the modifier option, and to
> > > try
> > > and consolidate the core setup a bit.
> > >
> > > However, if having a completely new option is preferred, I am happy
> > > enough
> > > to do up a different patchset for that.
> > >
> > > > I scanned through the series, not much to say.
> > > > Maybe add a unit test for new cmdline option.
> > > >
> > > Sure. Once it's decided what approach (if any) to take, I'll do up a
> > > new
> > > patchset, taking into account any relevant feedback on this set.
> > >
> > > /Bruce
> >
> > Changing the EAL parameter parser to a "two pass parser" makes sense.
> > I think checking for existence of more than one lcore specification options should suffice; we don't need to accept multiple lcore specification options and check for conflicts.
>
> There already is a first pass to catch log parameters, could the offset arg be handled there?
>
It could, but I'd rather not get into further handling of args in a
two-pass setup. If we go that way, we might be better to do a completely
"delayed-parsing" setup, where we use getopt to put all arguments into a
structure with named pointers for each arg type. Thereafter we do the
actual processing of args from the structure itself, allowing us to do all
arg processing in a fixed/known order. Unfortunately, that would be a
significant change in how things are done.
Also, from the discussion on this thread, there seems to be some support
for having a completely new cmdline arg that takes the core list and always
remaps them, rather than using a modifier to existing args. Your opinions
on the relative benefits/drawbacks of the two approaches are welcome! :-)
/Bruce
More information about the dev
mailing list