> From: Bruce Richardson [mailto:bruce.richard...@intel.com] > Sent: Monday, 7 April 2025 12.41 > > On Mon, Apr 07, 2025 at 12:15:13PM +0200, Morten Brørup wrote: > > > From: Bruce Richardson [mailto:bruce.richard...@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.richard...@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. > > > > > > > > > > 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. > > > > When remapping, do we need to support gaps in the "lcore" (logical > cores) > > array, e.g. for secondary processes, or can it be continuous from 0 > to > > the number of specified lcores? > > > > And are new EAL parameters for this really beneficial? Doesn't e.g. > "-l > > 0-9@130-139,100@140" suffice? > > > Actually, I believe "0-9@130-139"[1] is not the same as > "0@130,1@131,2@132,...". The latter affinities one thread to one core > ten > times over, while the former affinitizes 10 threads to 10 cores - > leaving > those threads free to move about within the 10 cores specified.
Interesting. The documentation [GSG] isn't clear to me about this; a example there could help clarify. [GSG]: https://doc.dpdk.org/guides/linux_gsg/linux_eal_parameters.html#lcore-related-options If users are manually passing lcore parameters to the EAL, then I see why some sort of remapping shorthand is useful. IMO, if the mappings are relatively exotic, it should be acceptable requiring an external script to build a long list of mapping parameters and then invoke the application with those script-generated EAL parameters. This would reduce the scope to support relatively simple, common mappings. Could we expand the --lcores syntax to support common mappings? E.g. "0-9@130+" to do what I thought. The lack of "()" treats the entries individually (not as a group), and the "+" indicates auto-increment. A more advanced example: "0-9@(130-131)+", meaning lcore 0 gets cpus 130-131, lcore 1 gets cpus 132-133, etc. > > Just to confirm, I tweaked our helloworld example to print the cpu > affinity > of each core when printing. > > ./build/examples/dpdk-helloworld --no-pci --lcores '(0-3)@(30-33)' > EAL: Detected CPU lcores: 96 > EAL: Detected NUMA nodes: 2 > EAL: Detected static linkage of DPDK > EAL: Multi-process socket /run/user/11304126/dpdk/rte/mp_socket > EAL: Selected IOVA mode 'VA' > EAL: VFIO support initialized > hello from core 1, with thread affinity for cores: 30 31 32 33 > hello from core 3, with thread affinity for cores: 30 31 32 33 > hello from core 2, with thread affinity for cores: 30 31 32 33 > hello from core 0, with thread affinity for cores: 30 31 32 33 > > ./build/examples/dpdk-helloworld --no-pci --lcores > '0@30,1@31,2@32,3@33' > EAL: Detected CPU lcores: 96 > EAL: Detected NUMA nodes: 2 > EAL: Detected static linkage of DPDK > EAL: Multi-process socket /run/user/11304126/dpdk/rte/mp_socket > EAL: Selected IOVA mode 'VA' > EAL: VFIO support initialized > hello from core 1, with thread affinity for cores: 31 hello from core > 3, with thread affinity for cores: > hello from core 2, with thread affinity for cores: 32 > hello from core 0, with thread affinity for cores: 30 > 33 > > Regards, > /Bruce > > [1] This actually needs to be "(0-9)@(130-139)", and with "--lcores", > not > just "-l", there are actually different flags with different behaviours
