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Dario Faggioli
8e2aa76dc1
In Credit2 CPUs (can) share runqueues, depending on the topology. For instance, with per-socket runqueues (the default) all the CPUs that are part of the same socket share a runqueue. On platform with a huge number of CPUs per socket, that could be a problem. An example is AMD EPYC2 servers, where we can have up to 128 CPUs in a socket. It is of course possible to define other, still topology-based, runqueue arrangements (e.g., per-LLC, per-DIE, etc). But that may still result in runqueues with too many CPUs on other/future platforms. For instance, a system with 96 CPUs and 2 NUMA nodes will end up having 48 CPUs per runqueue. Not as bad, but still a lot! Therefore, let's set a limit to the max number of CPUs that can share a Credit2 runqueue. The actual value is configurable (at boot time), the default being 16. If, for instance, there are more than 16 CPUs in a socket, they'll be split among two (or more) runqueues. Note: with core scheduling enabled, this parameter sets the max number of *scheduling resources* that can share a runqueue. Therefore, with granularity set to core (and assumint 2 threads per core), we will have at most 16 cores per runqueue, which corresponds to 32 threads. But that is fine, considering how core scheduling works. Signed-off-by: Dario Faggioli <dfaggioli@suse.com> Reviewed-by: Juergen Gross <jgross@suse.com>
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